1) Make it more accessible to new players. The vast majority of your players are former OSI players. Clearly, there are people that are willing to macro for a week before they start playing the game. But a player entirely new to UO? They move on before they get to experience anything. I don't know what the solution is, but the entire newbie experience needs to be scrapped and reworked. Change the entire game for new players so they don't spend hours running away from skeletons without bandages.
2) A fun, rewarding endgame. Create something to do after 7x/tower/murder spree. Whether it be PvE or PvP based (both, in my opinion. UO PvP is driven by player interaction, and PvE hotspots create interaction), there needs to be something else. Boss fights, instanced pvp, it doesn't matter. Any sort of endgame would be an improvement.
You have the power and freedom to take existing mechanics and take the game down the path it could and should have gone. Go for it.