Iceman was confirmed for the next Advanced Pack a long time ago, Iron Fist will assuredly be in it too.
So that gives us (at least, assuming Doomsaw isn't lying):
Doctor Doom (VA: Lex Lang)
Kitty Pryde w/ Lockheed
Blade (VA: Khary Payton, They want to get Wesley Snipes, let's pray for an enhanced :lol)
Iceman (VA: James Arnold Taylor)
Iron Fist
Ant-Man, apparently Hank Pym's, (VA: Wally Wingert)
Winter Soldier
And likely:
Nick Fury, the devs constantly tease a desire for a "Nickromancer", he's a big name character, and already has in-game assets.
War Machine: Established as desired to be a separate character, not an Iron Man enhanced, got pretty far in mentions for most desired 2015 heroes, and they've been in-discussion for his mechanics already.
Elektra: Confirmed 2015, but she's also a 200 ES hero, so I don't think she'll be in the Advanced Pack. Taskmaster wasn't retroactively added, right? Same here, I'd guess.
Havok: Off-handidly said to be coming 2015, has in-game assets
She-Hulk: Likewise
Domino: Likewise
Spider-Woman: Said to be coming "late 2015".