I wanted to make this thread a while ago, but I didn't feel it was relevant back then.
So, we have created a few pools in the past which are based entirely on the existance of a tag at the pixiv source.
The earliest one I remember is pool #323 - Touhou - Let's Make Touhou Kids!
All images in the pixiv project are tagged "東方子作りしましょ！", which is essentially a pixiv equivalent of touhou if_they_mated.
Now, the rule for what goes in the pool is simple. Is it tagged "東方子作りしましょ！"?
Yes: include
No: don't include
These are the problems I have experienced with such pools:
1. They are essentially redundant with tag searches
2. Danbooru users don't care about the rule. Even after the project is finished, they add any touhou if_they_mated image into it.
3. Pixiv tags can be added by any user and pixiv users care even less than we do.
4. pool:323 bad_id: If a post is in the pool, but no longer on pixiv, you cannot tell if problem #2 happened or not.
I made this thread because of pool #7030 - Touhou Armored Warriors
with these 2 questions:
1. Do we want such a pool?
2. If yes, how do we enforce the rules and avoid the 4 problems stated above?