Given that characters have a choice of head types, I'm going to assume that hats and heads are combined on the fly by the game engine. Thus you can replace the heads without the need to update all of those hat meshes at the same time.

Meanwhile for hands, no such luck. SE would need to go back and update most of the gloves out there. This late in the game that's a lot of work.

Some improvements can likely be worked in with improved skin materials though. Perhaps dyeable nails falls into that.

One compromise would be to go with a new hand and foot mesh for some more popular items, the base player model and new items going forward but I'm not sure SE would be keen on that kind of inconsistency.