> what are the end user benefits of this massive API change (except the indirect benefits of having happier developers)?
I see two (very small) benefits: resizing windows may be prettier, and you can use a rotated window as if it wasn't rotated (except that it will be ugly due to the lack of anti-aliasing).
> The main advantage pointed out seems to be performance
Where did you see this pointed out?
Me, I didn't see claim of performance gain by Wayland developers and in my understanding there should be little difference: Wayland is very similar to the X DRI2 extension, so if the toolkit you use take advantage of the X DRI2 extension, then there shouldn't not be much performance gain with Wayland: fewer IPC due to the merge of the window manager and the display server/compositor, but about the same way to use the GPU memory.