Ya, the way I imagine it is just inherent unlimited clickable abilities tied to gear, that draw on some kind of resource (mana/focus/whatever).
You limit the possible ability build combinations by only attaching certain ability types to certain gear slots. Like, all CC abilities are found on head and glove gear exclusively. Say for whatever reason the developers don't want players to be able to do big crazy nukes and CC at the same time... Just make the big nukes come from the same slot CCs come from. Then the really desirable items from the end game could be unique abilities found on off-slots. Like OMFG crowd control boots. Then it'd be possible for a high end character to have 3 CC abilities etc etc. Limit number of gear slots to something like 8-10, so your character only has access to that many potential abilities and has to make meaningful decisions.
Under this system you wouldn't need levels... Stats... AAs... Or any other form of character progression. The whole game would be acquiring these artifacts, and each one would be very meaningful and have huge impacts on your character's play experience. You'd be constantly evolving if that's what you wanted to do. You could have a broad scope of abilities, or be able to focus in and become a powerhouse in a given situation.
You could hand craft every single item in this system... Since there would only be a couple hundred in the whole world. They would be difficult to obtain, and you'd carry them for months, and in some cases, forever.
