2/2 Improved Health Funnel is stupidly large amounts of healing.
A one-box warlock can solo most 5-man group quests at level.

I'd imagine, if you were willing to kill slow, you could use a Blueberry or Felguard to tank.
The issue isn't so much ability to survive (especially with a healer + health funnel), but more the capacity to hold threat while you dps with any kind of speed.
Also a pet gets much more of the masters stats now, with strong PvP gear you might have a high Resilience pet with massive health.
I wouldn't think heroics would be possible, but normal dungeons would be.

I'd probably stick to questing and pvp to level.
If you wanted to do dungeons, you might be better off with an actual tank type.
Or possibly something like an SL/SL build, built on drain tanking.

I'm running (infrequently at the moment -- other teams have my time) a 4x Affliction / 1x Discipline team.
They're only 22nd level, but quite fun to play.
5x instant-AoE fear, lots of dots/curses, holy nova, etc.
Might go 4x Demonology, while gearing up through pvp, until there's enough spell power to go affliction.
The team is about 20 dots on each target... )