It is a very wise idea. You have a potential to reach those wizards (if you haven't become one of them yet) ...
Read about LPC. Liberated Pixel Cup is a project of OGA you could see there assets with [LPC] part in the start of the
I don't think that itch isn't good for CC0 and collaboration at least when combined together. I saw many times when people set in metadata "it is CC0" but in description they write something like "no redistribution". And it is sad because I am one of the reasons that it happens... Most people on itch is about honor of an artist. Such people usually can't get along too long. At least if there will be one donation to the collaborative pack there will be some fights... And itch is more about centralization. Do you think it will live enough long with centralization? I like the way of lpc on OGA. There just a bunch of assets of different artist. with a [LPC] part in the name and it fits other tiles of this incredibly world.
quantity-over-quality
It is good to accommodate as many people as possible but I don't really think it is a good idea to sacrifice one style. It will more likely look like several packs merged into one and it would have sense if someone continues it but... It is again often against honor of creator.
“sci-fi top down rpg, endesga32, 24x24px”
I won't say anything specific about that except this emoji ≽^•⩊•^≼
thats 100% free to use and expand.
That's why I use only CC licenses for art and only open-source licenses for code
P.S In general I thought about it and want to do something like it. I really like this idea but I think we need something like in-between of follow style and do whatever you want while follow some very wide restrictions