I don't think this fits on the main site
While I understand that you want to put this somewhere more visible than Meta because one of the goals is to provide this to people who don't have the reputation to post a Bounty for the List of bounties with no deadline, among other reasons, I don't think your attempt to coerce your desired result (help people who want to see challenge X answered in language Y) into an accepted PPCG format (Cops and Robbers) was successful. There are some superficial similarities that you put in intentionally, I think they both detract from the main purpose, and at the same time they don't actually accomplish the goal. For example, I can't think of a useful "Winning-criterion" or even a reasonable way of scoring either side. The coat of paint that you tried to put on your idea to pretend it's on-topic was not successful, and I don't think additional paint can fix the problem.
It's still a good idea
Or, I like it at least. I would much prefer if all the weird Cops and Robbers veneer were completely ditched and we just abuse the Q&A format even more than we already do. Basically, every "answer" would just be a request, then if someone fulfilled the request they should indicate that they did in a comment with a link and the poster of the request can edit that link into their "answer" (This pattern is common in CnR, so it doesn't seem like too much of an abuse of the comment system to be acceptable). I'll admit that I'm often in favor of not adhering too strictly to "Stack Exchange must be Q&A format", but there are conflicting view points.
Without rephrasing it as a challenge, it could be on-topic
The main PPCG site isn't solely restricted to challenges. For example, "Tips for golfing in [language]" posts are hosted there rather than Meta, and there are occasional "Help with X" questions, some of which are considered on-topic. I wouldn't take those as sufficient evidence that this could just be posted without worries, but in my opinion it does mean that this suggestion would be equally on- or off-topic regardless of attempts to rephrase as a challenge. If it's not allowed on the main site then it would definitely be acceptable in Meta, though that runs into the Sandbox Problem where new users that would benefit most just don't see it.
Speaking of the Sandbox, I think that's the biggest evidence that this belongs in Meta. This strikes me as very similar to the Sandbox, and the Sandbox is very firmly in Meta. It's not indisputable, but I wouldn't try posting in Main unless there's a very strong consensus first.