Yeah, I would expect Sinnoh remakes before Kanto remakes or revisitation at this point. I think the whole Kanto 'dex is pretty much accessible in modern games now thanks to XY and SM, and the Kanto region itself is accessible via RBY on Virtual Console. At this point, Sinnoh and Johto are the furthest back in the chain as far as transfers go. You have to transfer from Gen 4 to Gen 5, and then from Gen 5 to Bank via the Poké Transporter to get Gen 4 Pokemon into SM. And the transfer from Gens 4 to 5 is rough since you have to play a minigame for every single Pokemon transferred, blegh. xP Plus if the tradition of a remake each generation continues, this would definitely be Diamond and Pearl's turn. Those games are 10 years old at this point (oh god the oldening ).
That said, I also would not be surprised if we don't get any remakes this generation, or if they do remake Kanto instead. There's really no technical reason to remake Sinnoh other than to make it prettier. Previous generations were remade because they were all on pre-DS hardware, making it either impossible or a pain in the ass to transfer old Pokes to new games. While transferring up from Gen 4 to Bank is tedious, it's still possible with all DS family hardware. They could easily leave well enough alone and move on to doing something else this generation, like they did with Black 2 and White 2.
Also, the Sinnoh games I'm not sure are as nostalgic to a lot of fans as the first three generations, even considering they're a decade old now. Whether GameFreak remakes them or not will probably depend a lot on how ORAS sold and how they would expect Hoenn to compare with Sinnoh in fans' eyes. Ironically, that's kind of a point in favour of Kanto remakes since those games are the biggest nostalgia cash-in. Bet a loooot of people would pay a lot of money to play RBY with glossy SM-style graphics for the settings and characters. Plus they set up Kanto in the story of SM, so... Then again there were a lot of shoutouts to a lot of regions in SM with it being the 20th anniversary of the franchise, so who knows honestly.
Anyway, sorry this turned into a rambly post. Just speculatin', thinkin' about future games for funsies. :V