I decided to give fixing the turbo mode for SNES another crack and I believe I've almost got it.
I could only test the roms I can rip from my collection, but here is a list of the bugs it fixes:
Super Ghouls And Ghosts - No more graphical glitches on waves or tower
Legend of Zelda - Buttons are correct while on map screen
Super Metroid - Bottom right of map now only slightly disappears during screen transitions
Super Castelvania - Did not see any graphical issues in first level
Super Rtype - Fixes issue where sometimes sounds would be bugged
Super Mario World - No more glitched pixels on bottom of reserve item box
Contra 3 - Loads with turbo enabled
The only game I tested that had any serious issue was Super Adventure Island, sometimes it would fail to load music. This is still a work in progress, but it seems like a major improvement, I'd like people to test further.
Here is a link to the build:https://ufile.io/qver8hro
Please let me know what you think, still trying to figure out the issue with adventure island and cleaning up code for a pull request.