but I do think a sizeable portion of existing C++ devs who don’t want to use rust exist
That may be true. But out of that pool of people it seemed that very very few wanted to work on the fish project. So it was not helping them much at all. The is a vastly larger pool of people that don’t want to learn C++ and some of those may be willing to pick up rust. It would not take much for that to out number the number of C++ devs that want to work on fish that also don’t want to learn rust. Given there are not a huge amount of contributors that regularly contribute to it according to their announcement blog post.
That is a bit more expensive and complex. Looks like this is configured with a couple of resistors for 5v from USB which is simple to get and a voltage reg to drop down to 3v3 optionally. Full PD requires a chip and active negotiation for higher voltage levels. Though there are chips that do that it does increase the complexity and cost and soldering skills a bit. Might not be worth it if all you work on is 5v or 3v3.