Spoilers ahead! Be warned....

Based on the body type and how old the person appears to be and going over who Zoom would keep in his prison I have come to the conclusion that the man MUST be another Barry Allen. Specifically John Westley Shipp's Barry Allen from the 1990 Flash show. My thinking is that Zoom wouldn't keep anyone else in his prison other than speedsters while he was waiting to find ways to steal their speed.

I've also been thinking about the particle accelerator and how Barry just isn't going 'THAT' fast compared to the comics. He's actually pretty slow. What if instead of another particle accelerator explosion they find a way to free the other Flash and he explains how he got his powers (VERY similar to younger Barry, just without the Accelerator) and they come to the conclusion that it's the Particle Accelerator that kept Barry from fully connecting to the Speedforce like he should have. So Shipp helps replicate how he got his powers to get Barry back his speed without creating more metas. This boosts Barry's speed by a HUGE amount making him as fast as zoom even with his speed from before.

Then Barry and Shipp chase down Zoom and fight him, this would probably involve Shipp sacrificing himself to save Barry and stop Zoom...so the season would end with Barry holding another parent dead in his arms (from his view, we know it's just a doppelganger) for a very emotional scene, then for the last minute of the finale he would talk to his dad about it....maybe talk to Joe as well in between. I think that would make a GREAT finale for next season!

All that said, I could be COMPLETELY wrong. lol