I think it's a good idea and there is probably a market for it.
I have a similar setup to what Eddie W. uses just a little bigger. I use a Miller Bobcat welder / generator for electric for power tools and / or welding in the field. Also have a 6HP 33 gallon air Sears compressor that will run multiple air nailers, impact gun, paint sprayer, portable sand blaster, cut off tool, etc. It runs at 135 PSI and only 6.4 SCFM @ 90# but has run everything I mentioned. I would consider building a 3 pt. driven compressor myself if I ever ran across a large enough compressor with a bad motor but really don't have a need or enough use for one.