Too many people now view healing in HPS. holy priest's have great utility and are still good and viable healers. if Paragon use holy priests i have to say its far from "broken" I would expect some sort of buff at some point but just because they are behind other healers in terms of HPS everyone jumps on the completely useless bandwagon.
We don't know much about 4.3 yet.
Blizzard may just surprise us all and fix all of the issues that make Holy ineffective. It shouldn't actually be that hard, because at the core Holy isn't a bad spec. It's just incredibly overshadowed by druids and rendered ineffective on current content by mana constraints and a lack of content-required raidwide cooldown. But Blizzard may yet surprise us and make 4.3 into an instance which matches the Holypriest's strengths. Weirder things have happened. I mean, reports say they have travelled faster than the speed of light now.
Been leveling as Shadow, easiest class I've leveled so far...it was hard with mana early on but when I got SWD it helped, heirloom trinket also helped, I don't think I've gone though Outland so fast on any previous (5) characters
I've found disc to be a fun leveling character and next to unkillable in low level BG's. 1k shield for 200 HP character ftw? As for DPS, at low levels you can get away with holy/disc smiting but I'm pretty sure around TBC you'll start to see your wrongs, shadow is the way to go.