Is it possible to parameterize a generic with a type that is itself generic?

In C++ I can write a template that takes a template parameter:

struct None;

template <class T>
struct FirstType {
    using type = None;
};

template <template <class...> class T, class Head, class... Tail>
struct FirstType<T<Head, Tail...>> {
    using type = Head;
};

This is impossible in Rust:

// doesn't work
trait FirstType {
    type Output;
}

impl<T, Arg> FirstType for T<Arg> {
//                           ^^^ type argument not allowed
    type Output = Arg;
}

But it's possible for the specific type:

struct Foo<T> {/* some stuff */}

impl<T> FirstType for Foo<T> {
    type Output = T;
}

I don't understand why we can implement a trait for any type T or for something like *mut T, but not for T<U>.

Is there any workaround?