I would definitely support that. Many of the recent additions to the standard library could have been done as separate libraries.
One example: I think the recent CollectionDifference functionality should have been prototyped in a library before becoming part of the standard library. I mentioned it during the review. Now we have threads with people complaining about the usability of parts of it, and the proposal author has to explain that it evolved like that over time. Again, not to point fingers, but it's worth getting actual experience using the thing from people who didn't write the implementation.
This seems to be my word-of-the-week, but that kind of process is just amateurish. Even if you've been working on something privately for years, if you approached the C++ standards committee without lots of real-world usage data, they'd laugh you out of the room.
Are we building this language for the long-term? If yes, then what harm does a 1/2 year incubation period really do?