Don't know for the other players but, for me, as skin like sherwood ashe, emerald taric,...and stuff like that are basically older version of chroma skin concept, I would much prefer if you create a brand new type of skin/chroma who will be "base chroma with small particle effect"
You can spot them from other chroma because of the unique (but simple)splash art and, in game, it give you a reason to buy them over potential futur base chroma of that champ who will not have those little particle.
Particle is just an exemple here (as they can be hard to show with champ like blitz^^) but they are other option to make a difference between those "old chroma" and the actual version.
A lot of those champ don't have recall animation in their basic skin like the newer one, maybe it's an option if you don't have plan to make recall for every basic skin in the futur (like the massive textuxe update but for recall :p)