I think what none of us can predict is whether or not a game world will be compatible with A22, considering the random world gen and lots of POI are getting added/updated, this might be a moot point unless you are playing on A21.
Oh, good point. Wasn't thinking about the 'want to keep' part, just renaming. But I think it's a pretty safe bet that worlds created now will not be A22/1.0 compatible.
This was when the gold version is released. I want to give them name that make more sense. I'm not going to be deleting everything with each new release any more.
Although, there is nothing keeping them from forcing us to delete old worlds with a "Special" new release.