I think it'd be cool as hell to take the Warrior Tier 3 set and (maybe) the rogue Tier 3 set, alter the stats and turn them into DK Tier 1 and 2 sets.
This means you'd be able to go back to Molten Core, and have a Death Knight attainable set.
I'm going to do some searching and see if I can figure out how to take these old sets, change the classes/stats on them, and add them to the monsters in the Molten Core's loot table. They need to have the exact same drop rates as all the other classes tier armor.
What do you guys think? The warrior/rogue Tier 3 idea is because from my understanding you cannot create your own sets, you must alter currently implemented ones? Also, the warrior Tier 3 set looks like a DK set anyway.. The rogue tier 3 was the next closest looking DK type thing I could find.
edit: I should add, for anyone who may not know, the Tier 3 sets were lost when Naxx was moved to WoTLK. Naxx was formerly a level 60 raid zone that dropped tier 3 armor, but was moved when WOTLK came out. Tier 3 sets are no longer attainable.
edit 2: Ugh.. doing testing for this I created a level 80 to kill a mob over and over.. the 80 got the achievements for realm first 80 and what not. Is there a way to reset that? =/