I thought about creating a .vsx version for VS2010. There are some benefits (beside mentioned by you), for example - using .Net 4.0 and improved WPF text rendering, TPL instead of using custom threads, etc.
But, there is one major downside - separation of development for VS2008 and VS2010. I'm not sure how to deal with that. I think that at some point I'll freeze development for VS2008 and switch to VS2010 completely.