Since I was summoned …
IMO cross-platformness of libraries should be a significant concern of the Scala Platform, insofar as it is straightforward to design for any particular library.
For example, let’s say we have a math library. In all likelihood, the API provided by this library can be implemented regardless of the platform. Better: there’s a high probability that the entire source code of that library would cross-compile without effort. In that case, IMO the process should favor and encourage a cross-platform library. Even more, it should probably question why such a library would be proposed without cross-platform support.
On the other hand, I do not think we should demand cross-platformness from a library addressing a concern that is not “trivially” portable. I/O might just be the ultimate example of this problem. Yes, some things can be made sort-of cross-platform. But in general, any I/O library design will make trade-offs when supporting multiple platforms. In that case, I would avoid holding it against the library the fact that it is not cross-platform. If it complies with the SP requirements for at least one platform, and is not provided for other platforms, it’s fine.