So the new 'look ahead' trailer shows Zoom preparing to take off his mask, either in front of Barry or in private as part of a post credit scene. So with the big reveal on the horizon, I would not only like to debunk popular theories that are lurking on the internet, but also state my own before the big reveal does happen (just for the sake of saying "I told you so" hahaha)
So let's begin with who I don't think Zoom can be:
(1) Eddie Thawne (both Earth 1 and 2) - Rick is currently starring in another show for starters, not thar it means he can't guess star in a single episode, he did appear in a dream at the beginning of Season 2. But I don't want to believe it's him for a number of reasons. (A) He died a hero, so why become a villain, (B) Earth-2 Barry is friends with him, as he appears on his speed dial, and (C) it couldn't be Earth-1 Eddie anyway as his death opened the wormhole in the first place, and Zoom had already been terrorizing Earth-2 for some time, unless Eddie somehow survived (or maybe wasn't allowed to die due to Eobard needing to exist during certain points in time)
(2) Joe West - lots of people thought it was him earlier on in the show, but I guess those people will have to rethink their theories now that he's dead (or is he? perhaps he used his speed to make his heart beat so fast that it flatlined)
(3) Henry Allen - I'm really really scared that this is the case, that Earth-2 Henry is indeed Zoom, however, Earth-2 Barry has a close relationship with both his mother and father (they're both on his speed dial and were planning to visit Atlantis - which would imply that E2 Henry hasn't got time to do evil things) there's also the fact that Zoom, who unmasked E1 Flash - and could clearly see that it was the face of Barry Allen - didn't exactly react to the fact that he could be killing his own son, and persist in plotting to steal his speed etc. This point takes me back to E2 Joe, who actually was on bad terms with Barry, so maybe a part of him didn't mind beating him up.
(4) Barry Allen E2 - the nerdy doppelganger's debut should be enough to discourage people from thinking that he is Zoom, but maybe that's the twist, he uses his nerdy persona as a cover for his life of crime. In 2x13 he was knocked out and locked up while E1 Barry disguised himself as his dorky counterpart, but perhaps this provided him with an opportunity to go out and do evil stuff again, like killing Deathstorm and Reverb before kidnapping the Flash and locking him away - it sounds kind of dumb but then again the Reverse-Flash was able to be in two places at once, with a version of himself still in costume somehow, so anything's possible when you're superfast. Another observation is that Catilyn, Ronnie and Cisco are all people who have helped Barry, so maybe the reason why their E2 doppelganger's are evil is because E2 Barry is evil, like an evil version of Team Flash called Team Zoom! Either way I don't think it'll be him, especially now that we have seen a snippet of E2 Barry helping the E1 crew find Zoom and even giving E1 Barry a heart to heart.
(5) Eobard Thawne E2 - come on, for real? Eobard as the bad guy again? also, considering how he's from the future, why didn't he choose to appear until AFTER the E2 accelerator explosion?
(6) Hunter Zolomon (aka E1 Jay Garrick) - I'm putting this under the 'can't' section because, well, no one from E1 can be Zoom because he was already wreaking havoc on E2 before the portal opened. But it feels like a waste, considering how ZOLOMON becomes ZOOM when you take some of the letters out. Maybe there will be a twist coming up, like Jay's real name is Hunter Zolomon and the guy we saw on the park bench was a speed mirage (although brining back that twist from the first season would feel kind of lazy)
So now that I've got all that stuff out of the way, time for me to ramble about my theories!
(1) E2 Wally West - our Wally from E1 is obsessed with speed, maybe that was the same case with Earth Two's... perhaps the power got to his head and he turned, you know, completely evil. Although Lonsdale was casted for having 'the heart of a hero' it'd be interesting to see him play bad guy as well, and that could give him more purpose on the show, maybe even teach him a lesson - he lives for speed but when he sees what he could have been like it could really mess him up. It would also explain why he didn't notice Iris or Joe while he was parading Barry's broken body on 2x6, assuming he didn't grow up with them then he doesn't even know they are family...
(2) Jay Garrick - he's been suspicious since the beginning, ever since that creepy speech in 2x2. He has even admitted very recently that Zoom actually never stole his speed, it was a result of his abusement of the V6 drug that Wells had helped him create. Not sure how that would work, Jay being a hero by day but a villain by night, maybe a split personality? or maybe just the perfect cover? Either way I'm sure there's more to it than meets the eye, especially now that Zolomon has been brought into the light.
(3) Hunter Zolomon E2- hear me out, the reason why Jay's E1 counterpart is called Hunter Zolomon is because he was adopted by the Zolomons. so if Jay was never orphaned on E1, maybe someone else was adopted as Hunter Zolomon, eventually becoming ZOOM - and to explore this thoery even more, maybe it's the alter ego of a character we already know, like a rogue perhaps...
(4) Jim Spivot - assuming they name Patty's father after the man from the comics, we haven't seen what Patty's daddy looks like yet. What if, just what if, Zoom removes the mask, and it's a face we do not recognise. Then one night, Patty and Barry are back together, he sees a framed photo of her father, and it's the same face... now that'd be interesting. Maybe on E2 Patty went to the bank with her dad and she was shot by Mardon instead. Jim is soul destroyed, and his loss of humanity is ultimately the first step for him becoming ZOOM, and it'd be cool if we could see his humanity being restored, getting to meet an alive Patty on E1 and suddenly starting to feel bad about his actions etc
(5) Daniel West - if E1 Jay is called Hunter, maybe E2 Wally is called Daniel, similar idea, except I'm not sure how it would work, maybe Joe and Francine had agreed to name their first son Daniel instead of Wally, who knows, anything is possible
(6) a character from Arrow - to enforce the whole crossover side of things, it'd be funny if Zoom transpired to be someone like Diggle or Brother Blood - we've seen an E2 Deadshot living in central city so maybe the same thing could happen again
That's pretty much all I have to say, this is obviously all my opinion and I'm posting it with hopes that I'll be able to parade my clairvoyancy, but if I'm wrong I give all of you the permission to make me feel like a total knob.
UPDATE: just saw a theory somewhere in the comments on a youtube video - someone reckons that the man in the iron mask (seen at the end of 2x13) is actually the E1 doppelganger of Zoom, and he put the mask on him to hide his identity, could be Barry's dad as we haven't seen him in any recent episodes