The list does not have to be arbitrary. At some point when there is enough games we can group them. Like horror games have their own list, tower defense their own ... and it does not even have to be an ordered/grouped list. We can still decide to just promote 3 games you like from the list with whatever reason you choose.
I don't understand the "joint efforts" part. Achieving this is already a big effort. What more do you want, an itchio-con?
I first thought about just giving 1 link as you said it "public collection" and for the same reasons you deliver I thought it won't be good. So this is why this idea is not a "1 link to 1000 games idea".
The easiest part is actually enforcing this. If a developer does not refresh his list lets say "every month" or does not promote others in their page or inactive for some reason, simply remove them from the list. Even if the person who is editing the list is gone someone from the community can just copy paste the last list and continue doing this.
Maybe it is spelled joined efforts. Just a different way of saying that several developers created something together.
I see it from a player's perspective. What do those games share, that I might be interested in them, just because I played one of them.
If they were indeed from the same creators, by shared past projects, they would have something in common.
But if the only thing they have in common is membership in the promotion club, I have reservations.
The games already share platform membership on itch.
A linkage could be, that developers try out games and do recommend them. Because if the dev of a game I like tells me, a game is good, I might be inclined to believe, that this could be true.
But the idea as I currently understand it, ist basically just a big list of members of the promotion club. You share the common thing of being indie devs and wanting to promote your games. Yawn. That is why y'all on itch, that is not news.
And if it turns out to be implemented like that, the recommendations of said dev I like are now basically worthless, if they are compelled to promote from the list or be expelled.
Also, horror games and tower defense games already have their own list. It is called tags on itch. Tag your game horror and everyone browsing for horror will have it in the huge big list of 40k games, that did so as well.
You want to bootstrap out of obscurity. In a way, I assume it can totally work with a custom related games club. I use related games and search similar games and such. (I even like tower defense games, but that is beside the point).
But what use would it be to take just anyone in, just because they asked? That's what itch already does. You need to have some sort of quality promise, and that might turn out to be a problem. As this saying goes, 90% of anything is garbage.
Or in other words, what benefit would a player have, compared to just randomly picking games from browse, tags and related games and even the game recommendations? Would they use those promotions, or be annoyed by them?
Curated games could be a huge benefit, because there are no public reviews on itch.
Many years ago, webcomics tried a similar scheme like you describe. I do not remember the name of that project. They would have a widget or whatever on the bottom of their page directing to two other webcomics in some sort of promotion circle. I do not know what happened to that project, but it has been some time since I saw such a page. Maybe I am not reading enough web comics, or the project died.