I think that if Hoenn appears in this generation then it will be at/near the end of it. An exclusive release on the 3DS is possible if it happens at the end of gen 5.
I agree with the last bit which is why it might be used to close off Pokemon on the DS.
After that, 2013/14 we might be seeing gen 6. After that is released on the 3DS then come the R/S remakes, or vice versa and R/S come first and then gen 6.