I recently stopped tanking, after seven long years, to become a healing Paladin.
It's pretty awesome...I have found my thrill for the game again! Of course it's nice only having one toon.
Anyway -- I start having concerns with healing and my original UI "CalaiUI". It was purely built for DPS and Tanking, not healing. So tonight I fiddled around to see about some ideas. I'm on a 30" monitor 2560x1600 so what may perceive to be "large" to you, is actually small to me because of the amount of canvas I have to work with.
It's a work in progress. Ignore the wMarker addon (I forgot to turn it off).
I'm thinking about using the far right side as an info box (threat, recount, and maybe some class specific stat info (like sp, haste boost, etc). I keep omen running so I can see who may be screwing up and about to take the blunt force of a nasty encounter--helps prepare me for heavy healing when a tank is about to bite it (I know, they shouldn't).
I got some more work to do, it's late and I'm exhausted. I did want to keep it friendly for tanking since I still have my tank spec as a secondary. I didn't want to go full blown healer mode and lose most of my tank necessities.
I have some ideas for borders and such -- so that might change here soon.
I could also keep it how it is. I'm not a big "flashy" kinda guy. I think for about 2-1/2 years I've ran with just plain black boxes around my things.