Gallium3D is cross platform - you could write winsys layers for Haiku or whatever, but OSX is one of Wine's main targets and I don't see them shipping Gallium3D anytime soon. Unfortunately no, it's not going to make things any easier.
This isn't really that exciting. Firstly it doesn't benefit Wine at all. Wine supports other platforms than Linux and other drivers than Gallium3D and Mesa and so this is useless to them, if that isn't enough the Wine source structure isn't built for this kind of swap out, specifically because Wine limits X interaction to a single DLL, winex11, and the WineD3D stuff doesn't have direct access to X. The Wine D3D developers have long said that a D3D state tracker won't help them.
Secondly, it's not gonna help porting games to Linux either. D3D is only one part of the DX API and a game does a lot more than just draw stuff. Arguably swapping out D3D for OGL is relatively straightforward in comparison to swapping out sound API, file IO API, network IO API, message handling, etc. etc. that's why some games allow you to switch between the graphics API.
Think of a womans body... reacts very well under multiple touches.
YMMV.
I tell them to turn to the study of mathematics, for it is only there that they might escape the lusts of the flesh. -- Thomas Mann, "The Magic Mountain"