I wonder if a spindle would really need the angular contact precision bearings. They are so expensive! I have some large bearings for farm equipment that are tight, no play/slop. I think they could work in a spindle. I don't think they could take 10000 rpms though. Maybe 3000 - 5000.
I'll be following this thread. I want to make a spindle for my router that can cut aluminum without the chatter. I think that just the extra weight of a "real" spindle would be a big help. The PC spindle is lightweight, I bet it flexes a little.