Something I love doing is taking on challenges from friends or from my own musings while walking the dog. For instance: taking my shittiest strings sample based plugin and try to process them to sound as realistic as possible.  Or take a synth plugin I've never used before, strip it down to basics and then twist knobs till I have something I like and base a track off of the new sound I created (a great way to learn how that synth works!). Write a song in a different genre than I've ever considered. Force myself to use a BPM that is waaaaaay slower than I usually do.  The list goes on!  Maybe there would be challenge threads specific to each sub forum?

If this ... feature, function?...  is added to the site, I really hope to see something positive and not separating. BT started giving out homework assignments on twitter at one point. He doesn't anymore, and I'm not sure when he stopped.

About the challenges themselves, perhaps some of them can be educational rather than zany? Even rudimentary. I was a fan of tribesports and their (very social) challenge system. The challenges were easily quantifiable... nothing was left to interpretation... so that may be a hurdle. Still, it was a very effective way to build camaraderie within the community.