Not quite sure where to put this and if it has been posted somewhere here already, but Yoshida actually addressed travel between dimensions in an interview on Saturday:

Q: Will we be able to travel between the First world and the Source?

A: It's possible with the WoL's power of the echo. It's an extremely convenient setup *laughs* but the echo allows you to cross between dimensions and parallel worlds. During the WoD arc in Patch 3.4, the former WoLs from the First world abandoned their lives to come to the Source, but there is a way to move without doing that, which will also be explained in the MSQ. You can think of it as something that amplifies the power of the echo. Relax, your WoL won't be dying *laughs* Once you've been there, you'll be able to teleport.

Source: https://www.reddit.com/r/ffxiv/comme...w_with_yoship/