Here is the RC6 for testing.
- The 4.10-rc6 announcement
- Linux 4.10-rc6 Released, Now Codenamed The "Fearless Coyote"
- Phoronix articles, reviews and news stories covering Linux 4.10
- Linux Git log
BTW, I was able to upgrade ubuntu MATE 17.04 PowerPC today.
Screenshot of ubuntu MATE 17.04 PowerPC with the new RC6: