In some of my own testing, I was only able to get rid of the frame 0 desync message by getting both players to start a brand new Dolphin folder with portable.txt, and I actually wasn't even able to get Wii Play to stay in sync until I fixed that frame 0 message. I still don't yet know which setting causes it. For Sonic Riders Zero Gravity, even if I got a frame 0 desync message, it would still play on GC controllers with no "real" desync.
Still, since you got things working, I guess there's not too much more for me to say about this. In my limited experience with this build, it's good enough for me on the few games I've tried even if it's not perfect. I guess eventually the ability to save online will be brought back but I have no idea how long it will be until then. I'm hoping when it does happen, there will still be an option to play online without saves, because for some games, it's less trouble for me to just stick with cheats.
Still, since you got things working, I guess there's not too much more for me to say about this. In my limited experience with this build, it's good enough for me on the few games I've tried even if it's not perfect. I guess eventually the ability to save online will be brought back but I have no idea how long it will be until then. I'm hoping when it does happen, there will still be an option to play online without saves, because for some games, it's less trouble for me to just stick with cheats.