For better or worse, I think Go sucked up a lot of the metaphorical oxygen for similar languages. Swift and Rust are in different niches and don't compete head to head with Go, so this isn't a real problem for them.

What I've long wanted is a better C++, not a better C. It would be hard for any such language to succeed today, because it will have to compete with Go, and Go has a fairly mature toolchain and widespread adoption and a lot of mindshare.

D literally is designed to be a better C++, and it hasn't really been a big success. Maybe that's because there really wasn't as big a demand for a better C++ as there was for a better C. On the other hand it may have been because Go sucked up a lot of the oxygen that D was going to need to succeed, and maybe that was because Go was a product of Google and D wasn't. (If this was my primary point, I'd make a more nuanced argument, though.)

I'm now wondering if the best way to get to a better C++ might be by piggy-backing on the Go toolchain. To get back to my original point, I'm wondering if Go might in fact be a good target for all sorts of better (for some definition) programming languages.