Faux kind-polymorphism in Scala

gistfile1.scala

object KindPoly {
  class Eq[A, B]
  
  object Eq {
    implicit def witness[A] = new Eq[A, A]
  }
  
  implicitly[Eq[{ type K = Int}, { type K = Int }]]
  implicitly[Eq[{ type K = Int}, { type K = String }]]               // Does not compile 

  implicitly[Eq[{ type K[X] = List[X] }, { type K[X] = List[X] }]]
  implicitly[Eq[{ type K[X] = List[X] }, { type K[X] = Option[X] }]] // Does not compile
  implicitly[Eq[{ type K[X] = List[X] }, { type K = String }]]       // Does not compile
}