This collab could be made like this:
Right now on hexquisite, you only see a part of the other hexes, this way you do almost anything you want, while having some guide to make sure the hexes fit with each other.
An improved idea could would work like this:
Everyone select the hexes they will do, they can select more than one, but the hexes they select can't be adjacent to the ones they selected.
They do those hex tiles entirely by themselvess doing anything they want (that follow theme rules and pallete rules) without posting the wip on the site.
After everyone make their tiles an image is made with all those tiles.
Now everyone must redo ENTIRELY their hex tile, doing whatever the hell they want (also following theme rules and pallete rules).
But when redoing their tiles they must MAKE REALLY SURE it fit with the adjacent tiles.
PS:This new hex tile they do can be something totally different from the old tile they made.
An image collab of the part 2 tiles is made and released.
The tiles made on part 1 are just something needed to make this project work.
So with this idea you will have freedom to do whateaver the hell you want, while still being influencied by others just enought to make the collab image works.
It would not work because after your part 2, everyone would again end up with a tile that does not fit with any neighbor tiles because EVERYONE redoes their tile simultaneously while assuming that the other tiles around them do not change. So to ensure that they would fit, the activity would still need to be sequenced during part 2 in a way that people would make new tiles taking turns and locking tiles that are done. In the end, tiles from your part 1 are wasted time/work and the adjusted part 2 (tiles getting done/locked sequentially) would just be how it already works.
You could axe part 1 and 3 entirely though and start with a yet more different part 2 where everyone picks tiles until all tiles are assigned and then have everyone do their tiles simultaneously with the added requirement that they need to contact/talk to their neighbors to really COLLABORATE on each of their 6 borders for each of their tiles. That would only work in theory though , assuming that people are actually good at communicating/collaborating/consenting on what they want to pixel in their shared areas along their borders. In practice though, people would probably just agree among each other that doing it sequentially works best.