EQ Never

You start the game as a Dark Elf (because they are awesome) and you run around Neriak doing Dark Elf shit. Stabbing backs, summoning imps, being sexy as fuck. But for a little bit you effectively don't have a class. You can use dark elf racial weapons and simple weapons while wearing simple armors, and you have access to the ability to hide and backstab as well as cast some minor necromancy/wizard/enchanter shit. Stuff that is paltry at best for all forms of progression, but all give you the option to pick your destiny, so to speak. So if you wanted to go the SK path (also known as best path) you would beat on shit with your simple weapons while getting hit with your simple armor and casting your shitty necro type spells. Once you reach predetermined plateaus within those skill sets, it tells you that to further progression in that combination of arts, you must forget that which doesn't fit into the mold. So dude picks SK and starts his unholy reign of terror and eventually caps all related skills that are determined to be "SK" centric.

Fast forward to a couple of months later. Dude decides he'd rather be a cleric for a change of pace, so he can, from his UI, mark the SK centric skills as "forgetting" and engages in combat again. He slowly gets worse and worse and his skills get worse and worse til he hits a predetermined floor where he can then re-open learning the skills of other archetypes. This gives him access to all the shitty rogue/wizard/cleric/etc skills and abilities again, so he starts casting Insignificant Healing and casting buffs or some shit til those specific skills hit the plateau, and then he starts learning the ways of the cleric. What happens is his old SK skill ranks slowly go down over time commiserate with the increase in cleric skills. Some skills can be flagged as unlearnable so you don't ever increase them, such as wearing a mishmash of light/heavy/medium/plate armor but only wanting plate skills to go up.

Or you could just make it so that you can't change classes ever. I'm ambivalent to the idea of changing, as when EQ comes out I'll play a SK and that's basically how that goes. It is just an idea to progress that concept.

you could easily remove them and instead move the con system over to a series of comparative calculations revolving around skill level. Hell, you could make the entire con system a skill of it's own, where you start at even+ mobs are "Looks tough!" and below are "Looks weak!" and eventually lets you gauge how difficult a mob is directly in relation to your skills. "This monster seems to specialize in magic, but your strength of arms is greater!" or "This monster could easily kill a small number of you without flinching. Bring friends!" Yada yada. Increases through killing -any- type of mob as you progress through the game. Ie, a tradeskill focusing individual couldn't tell an orc from a orc, but someone who has been out slaying things can.

For replacing the concept of levels.. well, original EQ sort of actually had that to a degree. The skill levels that were dependent on you leveling could instead be the source of progression, not an unlockable based upon it. Lets go back to SK guy. His "level" would be tied to his primary skills: Martial weapons (an average of all weapon skills, meaning more powerful SKs know all weapons and not just the one they were twinked with) Plate armor, Channeling and Spell School: Necromancy. As all these things rise, he would con more powerful compared to other players that weren't as endowed. Make skill gain tied to fighting enemies who have their own skill ratings and you can only improve to +5 to what they have. Orcs in the commonlands have good weapon skills but bad magic defense. Blowing them up with spells doesn't gain you shitloads of + necromancy, but attacking them with weapons has a higher max threshold than necromancy increases from them. Not a gigantic margin, but that could easily be added to the game in the form of having to hunt for dangerous game to raise specific skills. The evil lich could be the only way to cap your necromancy skill by basically getting into a dot/nuke/spell duel with him and chaining the fuck out of your spells. This would also promote group play if higher level spells can only be used by certain skill levels, and a group is required to effectively fight the lich long enough for the necro to get a point or two. This can be expanded into creating a raid or multigroup setup where the only way to get the very last point to open up Mass: Summon Corpse, which would drag an entire raid's body back to the caster at once is to let your necros blast the shit out of Dracolich, for example.

I'm just full of examples, but the idea is pretty cut and dry. NPCs (not just monsters) have skill levels that represent their general difficulty. You can increase your skills by attacking stuff that is either slightly harder, on par or slightly weaker than you are in that area, but when you go beyond their abilities, you have to move on. Instead of staring at XP bars, you would get "You can no longer progress your Spell School: Necromancy on this target" or if you really need to say fuck you to all hand holding that badly, just have it not increase and don't tell the player. We all love checking our stats constantly to see if something changed, right?

Have mobs progressively get more powerful in various skills as you expand outward from home cities, to a median level around hubs such as the EC tunnel or what have you. Throw in your random rape mobs such as griffons or sand giants, by having them have much higher comparative skill levels so that fighting them pretty much always spells doom for the lower skilled players. Combined with the Con system being a measure of how much combat you have been involved in, you could create that experience of "Is this thing -really- that much harder?" to "OH SHIT FUCK FUCK RUN FUCK OH SHIT!" Hell, even give NPCs of increasing average skill levels an innate negative to player Con skill checks. Is that Griffon really that much harder than an orc shaman? Oh yes he is, but he'll con the same to a low con skill low player skill player.

The more I think about it, the more I like it. Higher level players who outpace people might be able to con shit and be like "Oh this mob will increase my necromancy!" but they would need a group or something to fight it, with the next highest players nearby might be killing something weaker. Go help that group til they can help you. Going level-less seems pretty... intuitive, actually.

it has to exist. But, and I state this everytime I bring it up, it has to be inferior in all respects to group required content. Not group "recommended" content (shit that necros can solo in original EQ, for example) but shit that would basically fuck up a single dude for even attempting it at the intended level. Lguk, for example, would be a group zone intended for people whose aggregate skill level averages would be 85-90+% of the skill caps for the game (using Vanilla as a guide) while, lets say, Sol B would be a group recommended zone with soloable content at the entrance for someone in the 85-90%+ skillcaps. The camps/mobs further in would be pretty rough but doable by a highly skilled and really active player, but a group would eat them up and their loot would be better than the shit the entrance mobs drop but not as good as the shit from guk. The skillcaps of soloable content could be set to smaller ranges, so that people who solo would need to travel more than people who group and kill appropriate mobs. Then you add in rng for stuff and you have a sustainable system that doesn't shut out solo play for some classes entirely, yet still 100% rewards even just pairing up more than solo play at all levels, with full group play 100% better than solo/pair play at all levels and for all types.

Gear has skill requirements. Instead of Plate armor saying "Classes: Bard/Warrior/SK/Paladin/Cleric" it would instead say "Requires 190 Plate Armor skill." This is for non-twink caliber gear. Oh yeah, very light on the no-drop tag, but definitely include the "Lore" tag on some stuff that should be, ya know, lore. Then, for items that would be considered twink caliber, you put the requirements substantially lower, or non-existent, but make the item slightly less powerful than the content around it would dictate. If your Breastplate of Rape requires 190 Plate Armor skill and has +25 to stats, the Breastplate of Twinkage would require 50 Plate Armor skill but have +20 to stats. Or a click/proc/whatever that may not require you to be high level to put the piece on, but the effect doesn't go off til the required skill level is met. Lots of random shit to do with that, and imo would add a bit of flavor. If everything was dropable and everything was equipable by anyone as long as they were the right class, the people who come after the first wave of players wouldn't be playing even close to the same game as those that came before did. Mudflation has a way of fubaring progression styles.