Not really, if a library is stable and doesn't need any change it's likely that the developer will not bother to recompile it, or even will abandon it, making it unusable (unless you compile a new version yourself). You also need that all your dependencies are updated before you can upgrade yourself. I haven't touched Scala in a while so I don't know if it is still the case but it seems like a serious problem, in the long run it will be the cause of many lost libraries.

In Java you can use an old dusty library from 15 years ago without a problem.

It seems fine to me. And sbt has made cross compiling so easy. A library author can easily support many scala versions.