Personally, I already know I'll be happy with whatever the official announcement ends up being but, having said that, it is fun to play along. I don't really have anything original to add (what are the odds given the fact that you good people are much more well-versed in the music world than I) but I'll throw out some names anyway.....
Anathema
Dark Moor
The Gathering (sweet talking Anneke into participating a few songs would make a dream come true)
Unisonic
Unexpect (they throw everything at you live and it is a true spectacle to see/hear)
If lyrics not entirely sung in English were a non-issue:
In Extremo (they have a good catalog of music, much of which is quite catchy, and are a blast live)
Mago de Oz (I think I see a few of you picking up rocks to throw at me as I type this.... but they also have lots of catchy tunes and are a blast live)
Arkona (an oddball choice I'd love to see; the vocalist's energy alone could power Atlanta if its electric grids blacked out)
A group I would LOVE to see for the Wednesday or Thursday night shows would be:
Saga (a vast catalog, seldom tour in the USA, and I'd think their stuff is varied enough that at least some parts of whatever they chose to play live would appeal to the majority; and they are extremely talented musicians, especially since their original singer has returned to the fold)