The Case For: Though not supported by subsequent screen grabs, the original still of The Man in the Iron Mask allowed for the possibility that he has dark skin. Plus, Wally is a character whose Earth-Two doppelgänger we have yet to meet.
The Case Against: Would a Wally-Two reveal “blow our mind,” as promised?
HENRY ALLEN (of Earth-Two)
The Case For: Henry’s doppelgänger has been alluded to but not seen — maybe Zoom grabbed him right after Barry had that Earth-Two phone call with his Atlantis-bound mom? Also, the new reveal that Henry’s mother was a Garrick surely is meant to seed some sort of future storyline. Over there, is Henry the real "Jay"?
The Case Against: When tapping out POW code to captive Barry, wouldn’t the Man in the Iron Mask have gone with “D-A-D” versus “J-A-Y”?
The Case For: We’ve seen people die and then return on many a comic-book show, and Eddie did get sucked into the wormhole after taking his own (and thus Eobard's) life in the Season 1 finale. With Iris and Barry finally on the same romantic page (or close to it), the return of her fiancé — or even his Earth-Two doppelganger —sure would create conflict.
The Case Against: Why the mask?
Included simply because someone was going to make this tired joke. Moving along….
The Case For: Resurrecting Caitlin’s fiancé would have a certain “wow” factor, though it’s dampened by the fact that we just saw “a” Ronnie a few weeks back, as an Earth-Two meta-villain.
The Case Against: And it's a pretty damning one — the Man in the Iron Mask surely would have reacted more strongly to seeing our Cailtin in Zoom’s lair.
FUTURE BARRY ALLEN
The Case For: The series premiere did tell us that Barry goes missing in the year 2024. Is that because Zoom time-traveled to the future to snatch his rival, as part of some long game or insurance policy? Plus, revealing “another” Grant Gustin under the (powers-neutralizing?) mask absolutely has the “wow” factor the cast has promised us.
The Case Against: If Zoom has a Flash in captivity, why the need for Barry’s speed? Or did he already drain Future Barry?
The Case For: Some have suggested that the real Jay Garrick (played again by Teddy Sears, or by someone else — even another cast member such as John Wesley Shipp aka Henry) is trapped in the mask. Or, if you want to go further off the reservation, the “wow” factor is that it’s another DC Comics hero such as Hal Jordan (who has been half-glimpsed on Arrow).
The Case Against: All of the teases from cast and producers would seem to suggest our mind will be blown by the sight of the person, not so much their identity. And unless Tom Welling is playing Jay/Hal/Diana Prince….