What I actually miss in Vercel is the lack of exposure to the underlying AWS Lambda infrastructure, at very least similar set of languages should be supported.
Go is in beta for years, for a company that depends so much on Rust tooling nowadays, I guess it would be about time that Rust would graduate out of a community runtime.
Also, their containers are based on Amazon Linux 2023, so they could also extend the support there.
For me, I see that as they pivoted from the early days of multiple runtimes, are nowadays focused on nodejs and they kind of still support multiple runtimes, but are not keen on improving what is already there.