Zig is just doing vtable-based effect programming. This is the way to go for far more than async, but it also needs aggressive compiler optimization to avoid actual runtime dispatch.
Well... effect programming using vtables. I think this is an emerging paradigm, but it is very early yet so it's difficult to define precisely.
My primary inspiration for the concept is theorem proving languages like Lean in which typeclasses ("interfaces" in the OOP terminology) are implemented using structures passed down as arguments ("vtables" in the OOP terminology) separately from any receivers (values of the type implementing the interface, which doesn't actually need to exist for Lean). Typeclasses (and interfaces) are an effect, albeit a simple and limited one. Lean can't express effects in their generality due to totality requirements, but the same mechanism would work perfectly well for effects too. As for the "vtable" aspect: the primary distinction in implementing typeclasses using exposed vtable passing is that the language does not in any way limit the programmer to zero or one implementations of a typeclass per receiver type(s) (cf. orphan rules in Rust, cf. compiling effect systems to witness-passing, etc.).