OK, so you’ve already reconstructed most of the BeOS API.
I’m sure that an X11 port to Haiku has already been called for, even though BeOS already had POSIX compatibility.
And I’ve already mentioned XUL.
So has anyone thought about a Win32 emulation port (like WINE for *NIX) to Haiku?
What other APIs have been considered, at least for Haiku on x86?
I'm sure that an X11 port to Haiku has already been called for, even though BeOS already had POSIX compatibility.
X11 is NOT POSIX… I’m sure someone will attempt another X11 port for Haiku - but I’m not sure it would be terribly useful. Better solution might to be port GTK, QT and other commonly used toolkits that exist for X11 - in order to help port apps that rely on them. Of course, this is just a stepping-stone, as it would make a LOT more sense to have apps written natively for Haiku in the first place.
So has anyone thought about a Win32 emulation port (like WINE for *NIX) to Haiku?
Been mentioned a bit actually. There is also an old BeWine port that is far, far out of date… I believe this would be a neat thing to have for Haiku too 
But I’m not holding my breath.
Reviving BeWine would be a nice project. However, I do not think it should be one the Haiku team tackles. At least, not yet. Getting a stable Haiku release should be the main priority. I know that I do not have the technical know-how to do it, but anyone could join the BeWine project and get it going again.