[C++] can't we use compile-time 'variables' in consteval functions as template parameters?

Reference:
https://stackoverflow.com/a/70905771
P1306 : Expansion statements 
tracking: https://github.com/cplusplus/papers/issues/156

// Returns the nth type in a parameter pack of types (ommited for clarity)
//   template <std::size_t N, typename...Ts>
//   nth_type{}

template <typename... Ts>
struct Typelist{
    template <typename T>
    consteval static std::size_t pos() noexcept { 
        for(std::size_t i{}; i < sizeof...(Ts); ++i) {
            using TN = nth_type_t<i, Ts...>;
            if (std::is_same_v<T, TN>) 
                return i;
        }
        return sizeof...(Ts);
    }
};

• Doesn't matter that i is guaranteed to be evaluated only at compile-time when its value is known in an abstract sense.
• Doesn't matter whether the function is consteval or constexpr or none of these.

The language is still statically typed and nth_type_t; must in any given instantiation of the function refer to exactly one type. 

If i can change in the for loop, that is not possible to guarantee. The language requires that the expression i when used as template argument is by itself a constant expression, independently of whether the whole function body can only be evaluated as part of a larger constant expression.

But i is neither declared constexpr, nor declared const with constant initializer.