On some places Flow is advertised as following LQT. So I would expect that there will be some kind of migration from LQT to Flow?
Topic on Talk:Flow Portal/Archive2
We are hoping that this will be able to be done but at this point in time we have not scoped work regarding a migration path.
I can't guarantee this, but I assume that a migration path will exist.
Migrating from the current (bare-wikitext) system should also be possible. I've outlined the rationale and use cases in another post.