I also leveled my paladin as a shockadin all the way to 85.
Mists of Pandaria comes along, and I figured, why let the 5 levels to 90 stop me? Guilded paladins had told me I should go retribution, that the pre-MoP shockadin excitement wasn't going to pan out. But then I happened upon the "Not Mad, Just Disappointed" shockadin spec by Catulla of Flavor Text Lore.
I've styled my paladin in this flavor of shockadin, and I've been having a blast. I don't have the holydin expertise to comment on whether shockadin really could be viable for Challenge Modes or PvP. However, I highly suggest trying this out if all you want is a little healer-spec mob-killing action.
Mists of Pandaria is here! The level cap has been raised to 90, many players have returned to Azeroth, and pet battles are taking the world by storm. Keep an eye out for all of the latest news, and check out our comprehensive guide to Mists of Pandaria for everything you'll ever need to know.