I can kind of see wondering about how many more releases there might be remaining for iOS 10, but the total number of betas remaining for all future iOS 10 releases, that seems like a much less meaningful thing (and perhaps even less predictable really).Well lets do this logically. 10.3 will probably have 7 betas. 10.3.1 may go into beta and can have 1-4 betas.
So that would be 11.
Now if there is a 10.3.2 or a 10.4, then that number doubles. So we could potentially see 24+ more betas before the release of 11.0 Beta 1. But it could be like 8.4 and we see betas for iOS 10 after 11.0 beta 1 was released.