thanks for asking! here's a top-three list in order of priority, with some explanation.
1) buff/debuff sorting and scaling, especially on player/target
this sort of feature is amazingly helpful for DoT classes (colorize their own debuffs, grayscale for others) in large-group environments. it's also of paramount importance for healers and anyone concerned with removing hostile effects. my biggest complaint with the current ui options as a healer is that debuff sizes are so small and not sortable, especially in operation frames. on that note...
2) reduce the chrome in operation frames
there is so much wasted space in operation frames. names can be written over health bars. corner icons can be enabled for key effects (force armor, rejuvenate, SRM, etc.). debuffs can appear with larger icons in the center. many healers have probably become accustomed to this kind of layout thanks to some other MMO that we won't mention, which has a whole host of excellent unit frame addons.
3) focus target cast bar
an easy one, right? we have cast bars for player, target, target of target, and companion, but not for focus target. please add this; it makes the focus target modifier key infinitely more useful!
some other requests, much lower priority:
- a threat meter (or "current threat on target" meter)
- focus target's target window (i loved this in that other MMO)
- mouseover healing (wait, what?)
- increase height of player/target frames
- remove chrome from quickbar frame #1
- one or two more quickbars (yes, really)
- item set swapping feature (actually a much higher priority than a lot of this stuff)
- ability to scale secondary windows (inventory, character, crew, etc.)
thank you for your consideration!