A week or two ago I was in #banshee chatting and posted a link to an album of some OpenVP screenshots. The developers were interested and asked me if I would try embedding OpenVP in Banshee. I have since submitted a patch that adds an interface that PlayerEngine classes can implement to become a visualization source, and also implements this interface on the GStreamer backend.
Once OpenVP is library-ized there will be a second patch adding an OpenVP extension, which will make Banshee do something like you see in the above screenshot. Probably not exactly as you see it there, since I'll probably want to "take over" the Now Playing window and render there instead.
Basically what I'm saying is that all the ugly plumbing is done and right now it works. It just needs polish, and hopefully it'll be ready when Banshee 1.0 is.