Even IF they ever re open the now congested worlds for transfer again in the future, why would anyone ever go back? Sure a few might but there are several things that would probably stop the majority of players from transferring back over.

1. I think it's safe to say transfers back would not be free.
2. Players are locked from transferring again for at least 3 months, probably longer depending on how long the worlds themselves stay locked.
3. Pretty much goes along with 2, with players having been on their new worlds for so long they will likely have made new friends, joined new FCs and LSs and have personal investment and not want to move. (Pretty much the main reason a lot of people still don't want to move off congested worlds.)