More operators inside `is(...)` expressions

[Per Nordlöw]

On Sunday, 23 August 2020 at 22:45:10 UTC, Steven Schveighoffer 
wrote:
> But this is definitely a much more drastic change than just 
> allowing != in the existing is-expression. I imagine the 
> changes to the compiler would not be simple for this.

I guess Walter wants a distinct syntax for compile-time 
expressions. `X is Y` is already used at run-time.

Is this related to context-independent grammars?