Perhaps, but I think a large part of this is designers assuming the scrollbar isn't actually for scrolling anymore, and treating is as simply a position indicator. Which for users who exlusively use a trackpad/touchscreen/scrollwheel for scrolling, it is. Ignorance tends to be the largest cause of accessibility issues.
It would be extremely useful for touchscreen users as well, a scrollbar lets you scroll a whole document (and go near specific points) in an instant instead of swiping like an idiot for a minute.
And for trackpad and scrollwheel users it's the same, I absolutely adore chiral scrolling but you still need to use the scrollbars sometimes (or often).
All these things only replace the arrows of scrollbars (enhancing them with some speed control), but the arrows are just a tiny and stupid aspect of scrollbars (I don't remember ever seeing someone using them).
