[unbound-method] Should prevent conforming to a bound-style interface method with an unbound method

interface Foo {
  unbound(): number;
  unboundOk(this: void): number;
  bound: () => number;
}

function what(f: Foo) {
  const unbound = f.unbound;      // lint error 
  const unboundOk = f.unboundOk;  // no error 
  const bound = f.bound;          // no error 

  // console.log(unbound());  // runtime error (expected)
  console.log(unboundOk()); // runtime error ❌
  console.log(bound());     // runtime error ❌
}

class Example implements Foo {
  x = 3;
  unbound() { return this.x; }
  unboundOk() { return this.x; }   // no error  (TypeScript issue rather than typescript-eslint issue?)
  bound() { return this.x; }      // no error  (this issue)
}
what(new Example());