There was a 70s science fiction future where customarily both parents adopted a new last name when they married. Seemed the obvious sensible policy for women's lib without a 2^N name-length scaling with the generations.
I only know one person who's done that. In some ways there's been less future shock than we expected.
I know a couple who combined half each of their original surnames to create a new surname. I thought it was a cool idea, but of course won't work for everyone's names. Their "invented" name turned out to be a fairly reasonable surname that is probably in not-uncommon use in general, so that worked well for them.
I feel like that could kinda work for my wife's name and my name, but the possible new combinations still sound a little off to me. (We both kept our original surnames.)
Villaraigosa did this - the former mayor of LA. He got divorced and kept the name, so hard to say what happens down the line there.
I tried supremely hard to merge my partner's last name and my own but each iteration sounded multiples worse than our own last names. We've kept our original surnames and given our kiddo a hyphenated one.
My partner and I did exactly that. She let me choose. Ended up with the surname from one of my favorite literary characters. Changed my first name to match as well. Happened to be a childhood nick name anyway, so I've always answered to it.
They divorced before I met the one. Whatever the reason might've been, it'd be something like this, so why ask? Eh, anyway. It's cool that more of these cases have come up here.
I only know one person who's done that. In some ways there's been less future shock than we expected.