This is basically the single, most anticipated and most basic feature I'm dreaming for.
Collections aren't really a good workaround for this issue, for number of reasons: most importantly their scrolling UI, limit of games being shown and the sole fact of being separated from the main game list. Neither me nor my girlfriend want to use them for this purpose, and as we sometimes make games together, it already happened that we fought with each other over this issue :P
Anyway, we're making duplicates of game pages each time I jam with other people with active itch account now, and it's a major PITA. Some other people don't care that much about their itch.io presence, but they probably would if only there was an easy way to make the game page I made appear on their profile. I really hope it will finally get implemented properly - I'm waiting for it for years now, ever since I've created my account. I was excited to see game admins feature appear one day, but sadly it turned out to be completely useless for this case :(