James Franciscus
Kick Henry Jackassowski
Let's not even talk about blues - someone could mashup hundreds if not a coupla-few thousand I/IV/V's
It's much harder to mash up. Blues is bigger than people realize. The hacks are killing blues day by day, but it has more variety than what's seen at your local blues jam. Try mashing up North Mississippi Blues with Jump and the minor West Side Chicago styles. It doesn't work.
As much as I can't listen to more than three songs, there's something about modern country that I find compelling and musically academic at the same time. I would love to write in that genre just as a fun experiment.