I still believe that Ash's Unova team will not change until the end of the Unova League. If the writers have Ash use his Unova team after the competition, however, I can only see his Snivy evolve. I doubt Scraggy will evolve unless Axew will evolve too (and right now it is extremely unlikely that the writers will make Iris's Axew do much of anything). The writers are probably not going to have Oshawott evolve because of its mascot role. Palpitoad probably won't evolve because of the "Water-type curse" that the writers started in Johto. I can't see Pignite evolving into its final stage, either. And Ash will probably not trade his Boldore, so it will never evolve again.
Lapras in the OI saga, although he had released it. But the other instances you have mentioned were accurate. The writers are giving Ash pokemon with greater variety in type in each saga.