We are on the Treasure during spring break and figured our chances were slim to none, but I happened to check in the wee hours of the morning when they released two HA cabanas exactly two weeks before sailing. (Both family cabanas—one Sandcastle and one M&M Cove.) I’m assuming they hold these for people with accessible needs, then release closer to the sail date if they haven’t been booked. I was shocked to see cabanas available after weeks of daily checking and quickly snatched one! Is it likely you’ll get one? No. Is it impossible? Also no.
Also, I was surprised that the cabanas were available online and didn’t go to some sort of “concierge waitlist.” Maybe there was no one on the waitlist, but I find that hard to believe, especially for a sold out sailing?