Minecraft developer here. The Graphics Team is still hard at work on this (it ended up being a ton more work than initially anticipated). The graphics part of our engine was quite honestly simply not built for this, and when we tried to put all the new features in piece by piece things went bad. Performance, even on the Xbox One X, was between bad and inconsistent during all the internal play sessions we had.
It will come, but we don't have a date yet. The gameplay team has been hard at work on the Update Aquatic, while the rest of the Engine team has been working on the Switch release alongside fixing performance issues on Xbox One. Those fixes are much closer than Super Duper :)