i can see eevee evolving into a ghost type with dusk stone, and a he could evolve into a dragon type at the dragon area in johto, and he could evolve into other forms by having max friendship with you and having a specific pokemon type right next to him in the pokemon lineup. or they could just create new stones and they could create shards from the stones the make glacion and leafeon.
The problem with most of those ideas is that they already exist currently, so they couldn't explain why they wouldn't be usable in the current gen. it's why then invent new evo items for old pokemon to evolve into new ones.
They currently exist, so why not add on to them. Yeah, new ways of evolving are okay. But what were you talking about.