If that is the only impediment, I will switch to GPL tomorrow.

I suspect that there is more than that. I suspect that people no longer like the GPL. I am actually one of those people.

My intent with WinFsp is to allow any open source project to use it without restrictions (commercial or otherwise). The only thing I want to restrict is closed source commercial uses (in which case I offer a commercial license).

Unfortunately I am not aware of an open source license that is compatible with other open source licenses and does not impose any restrictions on them. The only open source licenses that I know that allow unlimited open source use, also allow unlimited closed source use (which I would like to restrict).

If anyone points me to such a license I will be happy to consider it for WinFsp.