All of the breaches between Earth-1 and Earth-2 are closed (for now, anyway), meaning that people can't travel between them anymore. But what about the other worlds? We're dealing with the multiverse here, with 52 alternate Earths, so could the show now start to introduce those? Once you get into that realm, your head really starts spinning with possibilities - maybe it's Jay Garrick from Earth-3 that's in the mask, maybe it's Earth 17's Barry Allen as Zoom, it could be anything. But while that might not make all that much sense, the notion of them opening up the multiverse could. After all, if they can't travel directly between Earth-1 and Earth-2, then perhaps one of these other Earths now holds the key?