Looking to see if there's interest in such a check.

P0634, adopted for C++20, makes disambiguating dependent types using typename unnecessary in a bunch of places. For example:

template <typename T>
using foo_t = /*typename*/ foo<T>::type;

template <typename T>
/*typename*/ T::bar f(/*typename*/ T::baz param) {
    ...
}

In fact, there are cases even before C++20 where typename is redundant, namely on nondependent types:

typename /* <--- always redundant */ std::make_unsigned<int>::type f();

Such a check would allow easy migration to the C++20 feature and relieve users of the need to remember rules for where typename is or is not necessary.