Can we make mixin applications first class at the type level?

[sighoya]

Allowing

mixin template GenInt()
{
     const char[] type="Int";
}

void f(T)(T a)
{
     return;
}

void main()
{
   f!(GenInt!()) //or
   f!(mixin GenInt!());
   return ;
}

opens the door for quasi first class type calculus. Type mappings 
can be saved as strings and can be instantiated as types where it 
needs to be, e.g. passing two computed types to a trait function 
and determine their compatibility.

Why isn't it possible in D.

Further, why wee need to state mixin GenInt!() if GenInt is 
already a mixin? Isn't it just redundant?