It's not half-baked at all. I think it's a great idea, even though I don't know the innards all that well. If there are questions here on PM that I've never faced before, very often I research, test, research more, test, fail, cry a bit from frustration, research, test again and the odd time, I've found that I produced something useful I can post as an answer to someone else's question.
Compound that with two or more monks going at a problem, bantering and throwing ideas back and forth, and good usually comes from it.
I really like your idea. I like challenges. There are many other monks here (imho) that also like to work on challenges, and some like the environment where many monks are working on it, and they happen to be able to bridge ideas from multiple separate monks' replies into a great solution that benefits everyone (you said this earlier in this thread). In this case, it has the potential to benefit Perl/perl directly, so count me in, even though it may be a mountain of studying I may have to do (I've reached the summit of many mountains on foot, as well as tech/coding, and am always ready to learn more).
Doesn't matter what the 'weekly' challenge is... if opcodes don't get much traction, start another challenge, and leave that one in the queue. It can always be looked at later. Perhaps list a known bug once per week that as a collective, we can look at and help the p5p. Perhaps a couple of docs get thrown up once per week... we look through and make sure the doc says what the code actually does, or better, we write patches for the docs where we know tricks that may or may not be bugs (but will never go away due to perlpolicy) that others may not know about because it's not listed, or not listed prominently enough.