My question is how would you adapt EQ circa 2000 with modern day gaming technology?
Start with EQ1 classic (up to Velious) as a base point.
Add an auction house and group finder, but never add instances. Get rid of zoning between areas except when accessing other planes (or shards if a mega-server). Add GW2's deleveling feature (but harsher) and keep unique items (jboots, shrink wand) that are useful and found in different areas of all levels all across the world. Give the world more life (orc highway x10000...) with dynamic content. Get rid of overhead quest icons and as many other things as possible to increase the immersion factor. Have the NPC's engage you in the world to start a quest. Make the ui as simple as possible, one small row of abilities (6 to 10 max) and a chat window. A very limited 3rd person perspective and first person that actully works. Do NOT allow addons or access to the basic game mechanics. Keep the mystery.
Throw out 99 percent of the useless quests. Make the few quests that exist very involved and last for many, many levels (think epic weapon quest in EQ1). All quests give very useful items, gear or abilities, and very little xp for completion. The xp is earned crossing the world while killing the mobs in the way of the quest's objectives. Make some of the quest's objectives ONLY doable with a group or a very, very skilled / geared solo player. Make the most important quests open ended, with room to be added on to with expansions. Think of cliff hangers at the end of a story. This is what the "Ever" in EverQuest should mean.
Make leveling not so important by including multiple horzontal progression paths (abilities, stats, unique items, crafting, LDoN's AA levels, faction, etc) that also improve your character. So that somebody who has ignored horizontal progression and raced to max level is gimped and easily outperformed by a lower level toon who has covered all the bases. This slows down leveling and creates a more dynamic leveling experience.
Separate the world into casual and hardcore play. The casual areas have fast travel (once discovered), easy gear, low death penalties, and other modern conveniences. Access to everything needed (but not desired) is possible without leaving the safety of the core zones. Make the outer zones dangerous, hard to get to and lucrative (but not necessary) for those willing to take the risks. The border zones would have corpse recovery and harsh death xp penalties. And in the most dangerous areas, the possibility of losing it all. Make sure the playerbase undertands the concept and consequences of Risk vs Reward.
Add PvP but with multiple soft factions and only in specific border zones. Some of these pvp areas can be easily reached though and have more simplifed objectives, like battlegrounds, but not instanced. The more adventurous PvP areas would have resource control, like EvE. In PvE areas away from cities, anyone can group with anyone else. It is only in cities and pvp areas that faction is important (or when running into certain NPCs in the wild).
Add world building / changing tools that allow cities to be built and maintained in some dangerous zones. Somewhat similar to GW2's WvW where improvements are made to taken objectives. But start from scratch and include crafters, adventurers, etc (VG diplo?) to the required mix. Completed settlements would have housing, fast travel, vendors, new quests, etc. Clearing forests, digging real mines into mountains, building roads and tunnels could all be part of these world changing abilities.