Probably the most important decision is where to put the source code.
The .NET parts of MW v4.8 are on svn.mapwindow.org.
I think they should stay on that server.
v4.9 should be on mapwindow4.codeplex.com (this site).
MapWinGIS v4.8 is already on codeplex: mapwingis.codeplex.com
We can either move it back to svn.mapwindow.org or tag/branch the v4.8 version and continue on codeplex with v4.9 (different branch).