"I think the value of a CoC is merely to signal to people who have experienced abuse or disrespect in communities before (which would describe, I think, most women and people of color who have participated in technical communities for more than a short time) that the community is on their side when sexists or racists show up. "
If a COC becomes a baseline requirement for people to run projects and attract contributors, ISTM the people who don't care will just add COC's, and never enforce them.
You say "But, it does say, "We will excise toxic people. We will try to make you feel welcome here, even if you have been made to feel unwelcome elsewhere.""
It does not actually do that. It's one level removed from that. It's "we say we will excise toxic people.". It in fact, may be the case that you go to ask them to enforce it, and they say "sorry, don't care", even with a COC.
Then you are back to square 1. You essentially are trying to use the COC as a proxy for "communities that will care enough to put a stop to things" and i'm pretty much 100% it will not achieve this goal.