Predicates are great but most of the good stuff including privacy, proper subtyping and abstract data types came with Ada 83. Rust can't hold a candle even to Ada 83 imo.
How many would pay for a Rust compiler?
- Ada is only a small part of what Green Hills offers.
- PTC mostly isn't even a development tools company, their main products are PLM and CAD (WindChill and Creo).
- I think RR is a one-man company.
As for who would pay for a Rust compiler: probably not a whole lot of people unless that compiler has something special the offer that the normal compiler does not.
The same goes for a C compiler, there are Intel compilers that are supposed to be 'better', but as it turns out, in most cases not 'better' enough for people to pay for them. But even then, I would not be surprised if more people pay for the ICC than for Ada (but I would also not be surprised if the Ada compiler sales rack up more money than the ICC sales).