If you (ever) want to cooperate on adding support for a new toolkit or improving the current, then the best you can do is contacting me directly.
There are some general rules at least:
All metrics must be implemented in all toolkits.
All widgets or its' parts must be drawed the same in all toolkits.
If some functionality is not REALLY possible, then other toolkits should be made consistent with this one. Although in reality there is always some way to do things as needed. It's only matter of difficulity.
Toolkit backends should be made to work without need of patching code of toolkit and recompilation. However, if there is no other way, it could be used.