You can of course, but it is "beta" level which means not all of the runtimes will be update to date, things are subject to change, and there may be bugs. We also can't say when the beta will be finished, though we're considering wrapping up 4.1 with a lot fewer of the features than we have planned, just to get it a non-beta version into people's hands sooner.
In practice we update spine-unity very quickly once new features are ready (it's currently up to date with 4.1-beta). We try very hard not to make breaking changes even in beta, though we do reserve the right to do so, worst case. There are often bugs as new features often means we rewrite large portions of the app, breaking things apart and reassembling them in a better way. We do try to fix them rapidly.
Going back a version isn't great and risks data loss that may require manual fix up. 4.0 -> 4.1 adds sequences and some other things. Going back shouldn't be too hard, though it's still quite risky. If you use sequences obviously they can't work in 4.0, which lacks that feature.
