Good news - Just did some multiplayer testing on my current build of The Ultimate Unicorn Mod for version 1.9.4 of MineCraft, and things appear to be working as they should. I had to change around some code for flying and swimming horses, which took a bit of time to figure out, but it appears to be working now. I'm hopeful I will be able to release the 1.9.4 version next Friday.
As for 1.10, I haven't gotten very far in porting it yet, but from my understanding it's not that different from 1.9.4, so I have my fingers crossed that it will be an easy port. I'll get it out as soon as I can.
Moving forward, after the porting is done, there's a lot of clean up and document updating I want to do. One big change I want to make is to fix custom unicorns so that I don't need to make a new release every time someone orders one. This would also make it so that new custom unicorns would become available in the mod within minutes of being ordered, which I see as a big plus.
Another thing I need to fix in the short term is that I host some of the mod's assets (like the mod files you download) on Google Drive. Google Drive is disabling web serving at the end of August, which means I need to find a new place to put some of my files. This either means I need to find another free service, or start paying for a service to host files. If you have suggestions, let me know!
After that, I'm looking forward to new breeds and other exciting features.