I don't think Sylveon would need the "Kalos Stone". Sylveon is 100% going to be tied to the buddy system. I can see it being get to Ultra Buddy to evolve into Sylveon. Players who want it ASAP would pay for the poffins.
But Aegislash, Slurpuff and Aromatisse will definitely need a Kalos Stone
I dunno, I can see it being the Buddy system
and a Kalos stone (walk 20 Km then use Item or something) for Sylveon
As for others, maybe not all those guys. I think only the ones who evolved via stone or 'weird' evolution methods like Malamar (turn 3DS upside down) and Pangoro (Level 32 + having a Dark pokemon on team) would require a stone.
Conkeldurr & Gigalith were actually Trade Evolutions, (or 200 candy), so the two Fairies and the two Grass/Ghosts who evolved via trade in game may be the same here as well.
Heliolisk will be Sun Stone.
Florges evolved via Light Stone, so it'll probably be a Kalos stone. Same with Aegislash who evolved via Dusk Stone like Chandelure in Unova.
This was the smallest Gen to date, there may not actually be a whole lot that could benefit from a Kalos Stone. It may end up being something like this:
Kalos Stone - Aegislash, Florges, Malamar, Pangoro
Trade or Absurd amount of Candy - Gourgeist, Trevenant, Slurpuff, Aromatisse
Sun Stone - Heliolisk
Buddy + Candy - Sylveon (or Buddy + Candy + Stone)