Testing implicit conversion to template instance with is() expression

[via Digitalmars-d-learn]

Should this work?

    struct V(string s) {
    }
    struct S(int U) {
        V!"xyz" x;
        alias x this;
    }

    void main() {
        S!10 a;
        static assert(is(a : V!Args, Args...));
    }

With DMD Git master, the static assert() fails. Should it? Am I 
doing something wrong? How can I test whether something is 
implicitly convertible to any instance of a particular template?