Not the original poster, but here's a summary of what we know so far.
All new classes will appear in either a PH or a PG, after which they'll be expanded upon in a splatbook. Knowing the bard and sorcerer and swordmage will all appear in Arcane Power tells us that those classes must appear in either the PH2, FRPG, or both. Rich Baker has said there will be exactly one new class in the FRPG, the swordmage, and that the swordmage will not be duplicated in the PH2. That gives us all the information we need to conclude that the bard and sorcerer must appear in the PH2.
Mike Mearls previously gave us the first letters of all eight PH2 classes: B, B, D, I, S, S, T, W. Based on this new information plus what Wizards has previously confirmed, that gives us:
B arbarian - primal striker or controller
B ard - arcane leader
D ruid - primal non-leader, possibly a hybrid role
I ?
S haman - primal leader
S orcerer - arcane controller
T ?
W ?
What do we know or at least suspect about the final three? Well, Andy Collins has mentioned a divine controller in the PH2 who uses flame strike and the like on foes, and it's certainly possible such a character could be called the theurge (or perhaps thaumaturgist). Some of the RPGAers have talked about a potential primal controller called the witch, though I don't believe any of the designers have officially mentioned such a class yet. And as to the "I" class, it's worth noting that the divine splatbook will make its debut before the PH3, which means the final PH2 class is very likely divine. A couple of the designers have talked about a completely-new-to-D&D striker making its debut in the PH2 -- perhaps it could be a divine Inquisitor? That's only a guess, but a reasonable one, based on the evidence to date.