Remathilis
Legend
The predicate to creating a 2E retro-clone, obviously, is acknowledging that it is indeed not "just the same as" 1E.
Such acknowledgment, without equating difference with some absolute standard of superiority and inferiority, is all the "old school" asks -- and what the "new school" too often begrudges.
I see what you're doing.
By that standard, no edition beyond 1974 should be getting a clone, since they are all "imitations of the original" (as Dialgo puts it).
But since you asked...
1.) The Sphere system which allowed greater customization of priesthoods.
2.) The expansion of school specialization beyond "illusion" and including alternates to the "8 schools" in later books.
3.) Kits
4.) Non-weapon proficiencies
5.) Bards playable from first level
I'd go on, but I'm not sure anything else would meet your standards of "superiority/inferiority"