The problem is that your vtable would have to have a monomorphised copy of the generic method for each possible instance, this requires whole program analysis just to generate the interface — and even then I would not be surprised if you could generate calls which the compiler was not able to relate to the interface — and then you get to the potential size explosion of your vtable as it has to hold an unbounded number of methods.

Note that despite having much stronger static semantics and much weaker reflection than Go Rust has the exact same limitation: a trait method with a non-lifetime generic parameter is not dyn-compatible. C++ is the same, a template member function (generic method) can’t be virtual (dynamically dispatched).