Sounds like a good project to hack on occasionally while putting the majority of effort into improving the current implementation. In other words, some effort is warranted because of the benefits of sharing code, however, wine can always transition to the new layout after it has a complete and (mostly) correct DirectX implementation.
There's no reason the GDI and win32k.sys couldn't be going into the wine tree at the same time as improvements to the current system.
--tim