Eventually he'll put one or more of his Sinnoh team at Oaks to catch more (why else would they give hima full team so early on in the season?) The last time he had so many so early was in Kanto, and how many poke'mon did he end up catching after Squirtle while there?
Since he has Gliscor evolved, I'd say it, since he needs Staravia, which will at some point evolve too, to pop balloons and blow away smoke (although he uses it in battle a fair bit) and Pikachu, Turtwig and Chimchar seem to have made themselves permanant members for the team. I also can't see Buizel staying at Oaks either, but it will end up evolving, so will Chimchar.
Pikachu
Staraptor
Turtwig
Monferno
Floatzel
Gliscor/Snover/Riolu
I reckon he'll catch a Snover or Riolu to replace Gliscor, more Riolu because he already owns a grass type, even if Snover is part ice.