Besides the "pragmatist in pain" route to mainstream there's also the "benefits for free" route.

C++20 is a very different language than C, but it got to mainstream because at the beginning it was "C with classes". Typescript is similar.

Every company has a bunch of "early adopter" engineers. The easiest way for them to introduce something new at their company is by claiming that the transition will be seamless and free.

D partially tries this path with its C compatibility. But it's a rare C codebase that doesn't use function pointers or array pointer syntax. I don't think D had any choice but to abandon those, but it made this path a lot harder.

P.S. there's a third route: piggyback along with a market transition. That's how Java & Javascript & Perl went mainstream.