Generally, Shimano tends to be conservative in their ratings, and they tend to be the first to introduce a new standard. 16T seems to be it for now, but I welcome larger, as I like as few duplicate gears as possible, and 16T sure is a ton better than old 10T on 52/42, though 14T on 53/39 was also common. Of course, 1X has zero dupes, so additional development on wide 2Xs may have stopped.