Why can't templatized classes be aliased ?

[KeyboardRider]

with these simple types:

class Implementator1(T){}
class Implementator2(T){}
class Implementator3(T){}

version(1)
{
   class ChosenImplementator(T): Implementator1!T{}
}

version(2)
{
   class ChosenImplementator(T): Implementator3!T{}
}

version(All)
{
   class Foo(T)
   {
      ChosenImplementator!T Bar;
   }
}

Why isn't it possible, technically, to alias a template ?
(such like that:)

version(1)
{
   alias (Implementator1(T)) ChosenImplementator(T);
}

version(2)
{
   alias (Implementator2(T)) ChosenImplementator(T);
}

which would avoid to polute a templatized class with some 
compiler switches.
Would aliasing template make sense ?