Might work as part of a job guarantee scheme. Rather than being paid welfare benefits you can get more money by working on open source.

Edit: I mean from a society perspective you pay a tiny bit more for a real gain, without reducing labour from the private sector.

The problem is that most of that work is not something anyone can pick up.

Regardless of the coding, one would first need to be familiar with git or VCS in general.

Also, you would want people to go back to normal jobs when they can. This would lead to short stints for all employees which I've always found to be one of the best predictors of bad outcomes