I think having the CS of a slider be able to vary as the slider progresses would be pretty interesting, especially in addition to variable slider velocity. This could for example be used as an indication of suddenly changing slider velocity
I think this cannot work in terms of playability since the variation of sliders in a certain map or difficulty will be difficult to remember or even expect.I believe mapping community will add some rules to ranking criteria regarding unreadable variations and that mappers will find a way to make it work.
Of course, variable slider velocity could be un-sightreadable, but with this, it could become easy to show variation in slider velocity.you say that, but . . .