I'd add (Su) (M) & (Ex) tags on abilities alongside it. Whatever someone thinks about the way those were used for AoOs it was similarly valuable to have those sort of distinctions at times.Formalizing the idea of Touch AC was one of 3e's better ideas, given that there's always been situations in the game (in all editions) where either you or a foe is only trying to touch som,enoe in order to impart some effect or other.
If 5e took it out IMO that's a step backward.