Nah, Virgil'll probably show up in Kalos with a Sylveon. >.> (I've been expecting this since Sylveon got announced.)
There's been 2 even Generations... I don't think this even happened in Gen 2. So this is far from "tradition". The only times it happened that I can recall are Dawn's Mamoswine and Ash's Gliscor... (Gary had several Pokemon in Johto that evolved by new methods, like Umbreon and Scizor, but he caught his Eevee before Johto and both it and his other such Pokemon were never shown evolving and, aside from Eevee, were never even shown in Gary's possession prior to evolution.)
Aside from Mamoswine and Gliscor, I'm pretty sure all such Pokemon were actually caught in a PREVIOUS generation of the anime.