I may have passed over it, but I've noticed that if you initiate either spindash in the air, regardless of whether or not you have used your double jump, you lose it.
Darn, passed over it. Well, let me try to add something.
Not being able to shield cancel ASC is going to reduce the viability of FH and SH ASC mixups, as well as make the move more one dimensional, obviously. When I would play Brawlman, he'd get most of his grabs on me by cancelling ASC right in front of me. Now, if Sonic jumps and starts a ASC, shielding is completely safe. People who actually study the Sonic MU are going to be annoying once they know just how limited he is while spinning.
I didn't notice much of a priority increase. Mario's rapid jab still clanks with the spins.