I may look at some of the IGH with drum or disc options. The problem is that any older frame won't be set for disc tabs in the rear, though Thearpy does make a retrofit. The Nexus rollerbrake IGH may be an option as well.

I also like the Schwinn, for now at least, since it seems to be pretty available in my area and tends to be pretty cheap. I had considered a mixte frame, but availability won't be the greatest here. Cost there would be an issue as well. I am kind of sold on 650b for the wheels and the Schwinns seem to be fairly easy to convert.