The guys over at WOWInsider have a ton of new information about the new expansion. It looks like that the Death Knight will start at Level 55, with mount and gear. Lots more information over there too.
Since the DK will play a DPS/Tank role and everyone and the world will role one, I think I will either focus on leveling the Warlock or the Priest to 70 first. I don’t think the Feral Druid will play a very significant role in the new endgame dungeons.
Logically, the healer will have the most demand out of those 3 characters. So, I will quest with the Warlock and heal runs with the Priest until both are at 80. Druid will most likely wait.
And yeah, of course I need to try out a Death Knight. I’d rather experience the content first though. It is like back in the first days of BC: I did not spend time leveling a Draenei or Bloodelf, I focused on getting the Lock to 70 first.
A lot of good stuff seems to be in the expansion though, pretty exciting!