I'm honestly not at all familiar with browsers but I really do wonder if a custom language wouldn't be a reasonable tradeoff. It's not all that insane as that is a path that has been walked before. For instance FoundationDB has their own syntax to manage their actor system which just transpiles to C++: https://github.com/apple/foundationdb/blob/main/flow/README....

V8 also has torque which I think to some degree also fits into that type of mindset.