Impossible to predict. Maybe will get ultra versions, maybe we'll get a third version, maybe we'll get remakes instead. No one but Gamefreak knows.
A full roster is possible. So far the current stance is still to cull with each new game, so don't get your hopes up. But Gamefreak can always chance their mind. Personally? If the next games don't have a full roster, I'm out for good. Not gonna keep waiting release after release for shit that'll never come. Already did that for good 6v6 online.