Even though Sceptile would be okay with attack, sp atk seems more likely because of Leaf Storm and Giga Drain. A sp Atk boost would be better for it. I see Grass/Dark being more likely to happen
Swampert wouldn't get sap sipper its just too broken, i can see him getting sand rush or something like that for a speed increase as for stats he'll probably get an attack increase by 30 with both defs going up by 50 with no other changes. Sceptile will probably get either Grass/Fighting or Grass/Dark with an spatk and physical atk of 70 and a boost in defs in by 20 with a speed decrease in 10 probably with adaptability or chlorophyll.
I see your point with swampert. I just think Sap Sipper would be a very good ability for Swampert, making it one of the only pokemon with no weakness. I agree with your increase in stats. Swampert needs more defense. It could be a very good wall with Sap Sipper, and a very good option for a rain team.
Even though Sceptile would be okay with attack, sp atk seems more likely because of Leaf Storm and Giga Drain. A sp Atk boost would be better for it. I see Grass/Dark being more likely to happen
i was thinking physical just because it has more depth for it in terms of movepool and leaf blade was its signature move when it was first introduced, anyway grass/dark is more likely.
But Chansey already has an evolution in Blissey. Blissey is already very specially bulky and boosted stats would probably be defense, which would just be too powerful :O