I used to envision worlds like that, and wrote down the ideas for them in a notebook before realizing there was no literary market for an X-rated version of Gulliver's Travels.
If anybody else has fantasies like this involving alternate realities, feel free to post them here. Like if you've ever come up with an answer to the question "How could the world be a better place sexually for the person with greedy genitals?" Who knows, you might even see a very "similar" porno get made. A series perhaps about someone from earth traveling to and experiencing all these slightly different sexual environments.
For example, another such sex world was the one in which erections were life-threatening for "normal" guys on that planet, like a blood clot or a heart attack would be on earth. On that planet, boners were something that required emergency medical attention and the first woman who spotted an erection would begin blowing that dong with the same urgency you'd see from an earthling performing CPR to save someone's life. So as a visitor from earth, you'd quickly discover that all you had to do was drive to the mall, get wood, brush up against some hottie and act like you're having a stroke---she'd immediately pull down your pants and start to be a hero and save your life right there in the middle of Macy's as a crowd gathered round to cheer her on and offer their support. Then, if one of the onlookers happened to be hot, you could start looking over at her and mumbling incoherently and she'd rush in and take over working your dong like a good samaritan.
Let's see, what other alternate sex worlds were there again?...
Their was the one where guys had a "mating season" and only got wood during the summer months, but women were horny year round and relied heavily on vibrators to get them through the lonesome winters. There were rare men who could get wood any time of year, like how albinos are rare on earth, and the owners of these everhard dongs were hunted down by the female-dominated government and taken to secret mountain retreats where an endless parade of rich powerful women would pay top dollar escort fees to boink a real cock out of season.
And fear not, all you fans of the female orgasm! Some of these sex planets were for you as well! Like the one where women had EASILY ATTAINABLE 8 STAGE ORGASMS. So the trick wasn't for her to get an orgasm---she'd be having at least one almost constantly. The real trick on that planet would be to combine the 8 possible orgasm types in new and exciting ways. So sex partners would look like those frantic performers in the chinese circus who try to keep all those plates spinning at once.... only they'd instead be trying to keep various errogenous zones in a state of overlapping orgasmic delight.

I might add a few more worlds if I remember them.
Wouldn't concept-driven porn like this be hot?
Other ideas, anyone?