Not much discussion here about another class unique (in PHB1 form, anyway) to AD&D: The Illusionist.
If the Assassin makes it in for kumbaya purposes, why not the Illusionist? It's a flavorful, fun class that IMO never worked right as a wizard specialization.
Yet it seems very likely that the Illusionist will be done as a wizard tradition - and (big if) assuming they do it right, I'm okay with that. If instead it's just another watered-down specialist, I will sigh deeply and roll my eyes.
Why can't the Assassin equally well be done as a rogue scheme? What is unique to the (PHB1) class that couldn't fit there? Assuming that, as above, they do it right.
What's the rationale for kumbaya applying to one class and not to another?
It all comes down to the mechanical definition of class, specialty and scheme by the developers and designers.
If class X is traditionally 3 traits and aspect Y is 2 parts, then aspect Y cannot replicate class X.
If feature Z is supposed to be simple, then class X's feature cannot be made into feature Z.