Sinnoh was split in east and west, which was represented by Shellos and Gastrodon. In Gen V nothing special was done with Shellos, because the region wasn't really split in two. The Kalos region on the other hand is split in three area's: coastal, central and mountain. Could that mean we get a new Shellos form?
The three area's seem to be represented by the colours of the French flag: red, white and blue. We already have a pink and a light blue Shellos, so they could add a white one to the mix and have a Shellos for each area in Kalos. Or they could add a red and white Shellos and use the current blue Shellos, eventhough it's colour doesn't match that of the French flag. Or they could go all the way and give us three new Shellos: a red one, a white one and an actual blue one.
The various Pokédexes hint at different forms of Shellos per region, but so far only the Sinnoh region has them. Kalos could add up to three new ones to the mix, and the Ruby and Sapphire remake (if it ever happens) could add some new ones too, because Shellos and Gastrodon where intended to be included in R/S after all.