As of last month the cabanas on Seaside are still by reservation only, Royal suite still gets one included. I asked why they had not changed to first come like on the Evo ships and was told it's because they have fewer on Seaside class.
On our four night, spending time at Ocean Cay, about three were reserved the entire time by paying guests but at least three remained available for most of the time.
I did not see any butlers bringing "amenities" like snacks or a cooler with favorite drinks as they did years ago.
Oh, after viewing that video I wanted to add the Seaside Yacht Club pool deck loungers have all lost their cushions, making them fairly uncomfortable. In the cabanas they either had some thin pads or pads made from towels.