This is a fair point. I would hate spamming any maintainer. Most of these contributions will happen after the students have completed their curriculum and done 1-2 concept designs. [Apologies if I did not make it clear that I am just trying to replace the redesign projects -- not the new concept design]
At the same time, if I fork any repo of my choice -- I don't think we'll necessary work on the most important aspects. Reducing the chances of the design getting incorporated or the students getting any objective feedback to improve things.
Over the shoulder is often the developer explaining their decisions in the code, instead of the reviewer trying to reverse-engineer it, independently. It's just faster and has less resistance -- not necessarily better.
Problem with remote live reviews is that in a remote environment, it's harder to tell if someone is free or they are doing their own deep work.
Either the developer has to wait for the review to be done asynchronously before the merge... or ping someone to review their code through a screenshare and take away their attention.
But when it came to large complex codebase or problems that required critical thinking everything fell apart.