The decision on what to do for a big part depends on what OpenGL 3.0 actually is. From carefully reading the latest OpenGL 3.0 announcements and their forums I come to the conclusion which I'll explain below.
There are basically two new OpenGL versions named respectively: Longs Peak, and Mt. Evans. Longs Peak is a cleaned up version of OpenGL 2.x and Mt. Evans would add DX10 features. For a long time everyone expected Mt. Evans to become OpenGL 3.0 and Longs Peak to be some OpenGL 2.x version.
Recently Longs Peak has been announced as OpenGL 3.0. Due to time constraints they weren't able to add all the features they wanted to Longs Peak, so they have added Longs Peak Reloaded (OpenGL 3.1?) which will arrive 2-3 months after 3.0. Further the 'DX10' version 'Mt. Evans' will arrive 3-5 months after 3.0.
So it appears like OpenGL 3.0 is going to be a port of OpenGL 2.0 to the new object framework. All the sources mention that all fixed function stuff that can be done using shaders has also been removed. Further according to posts in the OpenGL 3.0 topic at opengl.org some stuff has been kept using integers because of backwards compatibility.
What does this mean for Wine? Well it seems like OpenGL 2.1 hardware like the Geforce6/7 can perfectly work using OpenGL 3.0. For DX10 functionality you ofcourse need extensions. Further it might mean that none of the DX10 opengl functionality will be ported back to OpenGL 2.x. Nvidia has done it but I'm not sure if ATI and others will follow. I expect them to add those extensions only to their 3.0 drivers. (Remember that ATI is working on a new codebase for their OpenGL drivers. This might be the real reason ..)
Roderick