I'd like to see some kind of mission system created for solo and small group players. Early on, EverQuest II introduced some instances that could be done both solo or heroic, but lately the content has become split such that the overworld is largely solo and instances are all heroic.
Its good to encourage grouping by putting the best gear in the heroic dungeons, and there are certainly a lot of quests to keep soloers and small group players occupied, but it would be nice to be able to do something besides questing when we don't have the time (or desire) to group with others. I vastly prefer dungeon crawls over questing, and missions in the various dungeons would be a great alternative to keep solo and small group players occupied.
The loot should, of course, not be comparable to TSO void shard loot, but providing soloers and more time constrained players with their equivalent of "elite end game" gear would be a nice way of continuing the EQ2 tradition of supporting every kind of player. Developers wouldn't even need to make all new zones to support this; recycling existing content could be a good way to bring that about without using up as much developer bandwidth.