This has already been teased by Grant Gustin, who told TV Guide:
What's fun about this show is that there's going to be multiple timelines as we move forward. I think we're going to start showing Earth-One and Earth-Two in the near future. There will be kind of different dimensions going on.
Having already played around with time-travel, not least with Eddies sacrifice likely to change both the past and the future, there could be alternate timelines where events are different to whats happened in the show. Earth-Two, mentioned specifically by Gustin, is as it sounds - an alternate version of Earth, and one used in the comics to explore multiple speedsters, so thats where Barry could travel and end up meeting