There is Kodi 17.1 final/stable available at PiPplware's unstable repo:
https://retropie.org.uk/forum/topic/6308/testing-kodi-17-0-stable-final-available-for-retropie
It is in the unstable because it needs newer firmware/kernel (which you can get with rpi-update), at least to play h265 videos. This newer firmware/kernel wasn't tested, by me very much in emulators, so if you do it, you have been warned. Newer firmware/kernel should come very soon to Raspbian and RetroPie.
Anyway, the 17.1 RC2 available in RetroPie is pretty much 17.1 stable/final like BuZz said, if the update warning appears just choose "no" and it won't appear again.