New to the forum (first post). Howdy peeps. I'm one of those crazy horse people that can't complain cuz Brandon created a super-horse, so I'm in love with this thread. I'm also in the middle of WoR, but I don't mind spoilers.
Someone above mentioned the Reshi islands were intelligent due to bonding with spren. I'm thinking I must have missed that part. I thought they were intelligent simply because they were much-larger-than-normal greatshells? I'm going to have go back and re-read I guess.
Anyway- back to Ryshadium... In the WoK, there were a number of descriptions of the interactions between horse and rider that indicated sentience. Which, in addition to the Q&A someone posted earlier, leads me to think that the Ryshadium are their own species, or race, on that planet. The horse's personalities indicated not just anyone could ride them, and they didn't need to be handled like a normal horse. I sort of liken them to Shadowfax from LOTR. Sort of the Lords of common horses that only grant permission to certain people to ride them. That's my 2 cents.