For Sceptile's case, no one is going to throw an electric type at it seeing as it already resists it very well...plus, it's "base" version is pretty damn fragile and I don't think it's going to be any more durable when it mega evolves.
Swampert I feel can't take advantage of Swift Swim due to how naturally slow it is...I hope the stats say otherwise.
I could see them doing well in doubles/triples, but in singles it screams bill of goods.
Those are fair points, however I don't necessarily look at it from just the standpoint of abilities, although I'm going to have to disagree with the usefulness of Sceptile's ability. Here is the way I see it:
1) Swampert- This thing already has good bulk and a decent attack stat, although you are right about it's speed, as long as it gets decent enough stat boosts to it's defenses and attack I don't see it really needing to take advantage of Swift Swim ever. It could end up just becoming a really good physical tank. It's already sitting on 100/90/90 defenses and a 110 base attack, and every mega gets a 100 point BST boost. Even if they don't focus solely on those stats and just give it 15-20 extra points on each stat (except HP, no mega has yet to get an HP boost) and then send the rest to speed. Let's say we do 20, you then have 130 base attack, and 110 d's on one of the best defensive typings in the game having only a weakness to grass, and sending the rest to speed would give it a 100 base...with swift swim. Of course the rest probably won't all go to speed, and some with probably go to Sp. Atk just for balancing purposes, but if we are talking those stats with even an 80-90 base speed, you can bet he could take advantage of it easy. Just to give a good example, Excadrill is probably the best abuser of Sand Rush (sand version of swift swim for those who don't know), and he is only an 85 base speed and has waaaaay less bulk and a worse typing. This gives me reason to believe Swampert could end up being just fine just from the base stat boost alone, he might no be able to abuse swift swim, but we won't know until we see the base stats.
2)Sceptile- Lightning Rod isn't going to really be abused from him being in, but more so on the switch in. You can team it up with something like gyarados to bait electric type moves and let it get the stat boost from it. He will need to already be in mega form to be able to abuse it, so more times than not he might end up be a lead just so he can get the evolution out of the way, kind of like Manectric so that it can abuse intimidate. I think he is another one who is going to benefit from just mega evolving though. His speed is already good and it will probably get boosted, and his special attack will probably shoot up about 30-40 points I think, plus he gets a pretty damn good typing that will help him resist a lot of good types. (Immune to electric, quad resistant to water now and resistant to ground)
