The devs have spoken about this. Quoting Nutomic:
Or you could just put a link to your old account into your bio. So this might be a useful feature, but very very low priority. // More useful could be import/export of settings and subscriptions (also much easier to implement).
So there are plans to address this in the future, so you don't lose your data from server migration, but migrating the account itself is low priority. (Even then if someone found a way to do this, and submitted a pull request, they'd probably accept it.)