The fact that the Eevee promotion will continue this year in the midst of the new generation hype speaks volumes. I'd be very surprised if a new Eeveelution weren't introduced in the upcoming Eevee short, and as you may recall, Eevee is a Generation I species.
Generation III was represented the least in the following generation, so in theory the same thing could happen with Generation V in this generation. Only a few Generation V critters need to evolve.But I feel that GF purposely left out possible evolutions for Generation V Pokemon in order to give more space for expanded evolutions in Generation VI. Like someone here already said, I feel like Generation VI will mimic Generation II when it comes to giving certain Pokemon more grace.