This won't be the "next" sexual, revolution but I strongly believe that at some point in the future gender reassignment will be such a straightforward and simple process that it won't even be called surgery anymore. I don't know how commonplace it will actually be but I think it's conceivable that humanity will go through cultural phases where people change genders frequently, and almost everyone has done it at least once.
Additionally - I foresee sex and conception becoming more and more uncoupled until the point where we rewrite our genome so that fertility is under our conscious control and contraception is no longer necessary. Perhaps we will even give ourselves the ability to lay a sort of "soft egg" that can be deposited into some kind of incubator, rather than go through the seemingly immense hassle of pregnancy.
On a more basic level, sexually, with the advent of firstly fully immersive virtual reality, followed by, perhaps, scarily lifelike sex robots, and eventually widespread, safe, and easy body modification by virtue of direct editing of the genetic code of adults, I think it's conceivable that a whole bunch of weird shit will come about that we would probably look at today as being wrong or dysfunctional... The Furries of today gradually transitioning into real chimerean practitioners of some kind of pseudo-bestiality, and people fucking robot or VR clones of their crushes, or celebrities that they've never met, for example...
Obviously there will be some real ethical problems to work through with some of these things (moreso the last thing I mentioned there, with VR sex clones of real people, the other stuff while it might seem strange to us today will just become a non-issue in time, I suspect).
I'm optimistic however that human culture as a whole will progress to the point where on the whole, people just care a lot less about a lot of stuff that today is taboo or cause for embarrassment or controversy, and accept that some people are just always going to be into weird shit. That said I don't doubt that all the cultural and technological shifts required to get us to this point will be preceded as they always are by the hysterical screeching of hordes of luddite, repressed, backwards thinkers about how this or that stuff isn't natural, it's wrong, it's going to lead to the breakdown of society, it's bad for The Children, etc, etc...
