I don't think any of those problems can be solved solely in the compositor - they all require co-operation between it and the actual apps. Which means, in practice, that you'd probably have to create an entirely new version of the Wayland API for creating and managing windows, add it to all the compositors, and get all the apps to use it too, on top of all the other work involved in fixing those issues. (This is the only real way to extend the protocol and has already been done a few times - the most recent one I remember was to add the ability to minimize windows.)