Im finishing up my 3rd 4 axis mill which is an IH and taking longer than expected. However, I have always been interested in a 5 axis machine and the possibilities of a diy model at home. I have seen a couple of model like the one at this youtube link, which I consider to be totally doable in a home shop. It's more of a 4th and 5th axis attachment but still gives you 5 axis machining capability.
"http://www.youtube.com/watch?v=DjPCEpZybXs"]YouTube - 5-Axis CNC Mill @ Hogeschool Antwerpen
There are several diy 5 axis mills on youtube.