I would like to flag openness for collabs too.

I am not sure how as these challenges are for all skill levels and a big part of them is to learn something new.
Randomized teams, and only let people willing to share, teach and/or be taught in.
Maybe randomize some teams around one pre-determined lead with more experience? I'm not sure.

It'd be cool to take it to a point where more research and development is necessary.
As has been mentioned there are problems around it. Time, effort, experience, version mismatches (funny how this should be a problem but it's reality). Communication and developing a pipeline could be part of the challenge though.

Sorry nothing overly constructive here. Just blurbs.