Wow, so many sets, and a good portion of them is quite good. Going to comment on some of those, and on the whole Rain discussion. I guess I'm stealing Xelacalle's post formatting since it's really awesome!
Gliscor, as Ginganinja argued, sure can KO Team 2 with ease right now, but cannot switch into Heatran since a burn will completely shut down it, and cannot really switch into Celebi either, since it will take 50% or more damage from an unboosted Giga Drain, and that's quite bad since it has no means of recovery. On the other hand, it has quite good type synergy with Meloetta, but right now it's not one of my favorite nominations for sure.
Thundurus-T is an excellent suggestion, maybe the one I like most (except my Heatran, of course), and was one of the reasons I proposed SpD Hippowdon back in the last round. Right now, Thundurus just wrecks Celebi and can cause serious headaches even to Heatran if you allow it to boost. It's also a Flying-type, thus have good synergy with Meloetta. Brilliant suggestion, I'd say.
I don't like those. They cannot switch in on Celebi without taking a good chunk of damage or being crippled by Thunder Wave. Mamoswine won't like switching into Heatran, either, and picking Adamant exposes it even to Breloom.
Salamence can kinda work, but it's checked so easily that Team 2 won't have many problems to be prepared for it. Just take something base 101+ scarfed with a SE attack and you're done. For example, Scarf Terrakion, which at the moment is also quite good against Meloetta-P.
Gallade is crippled by Heatran; it can work otherwise, it's just I don't like it that much myself...
Hydreigon is good, doesn't like T-Wave but can work even if statused. However I agree with Pocket, a set with Earth Power will deal with Heatran much easier, since Focus Blast is not exactly reliable, and a Roar by Heatran on a missed Focus Blast (heck, even if FB connects, since it only deals about 60%) is a quite large loss of momentum.
Heracross is a good suggestion, and I would really love to see it shine. However, it assumes rain and thus picking it is a dead giveaway we are using a rain team; while running Rain on its own can be good, forcing ourselves to do so too early can give the edge to Team 2. See the following point for more clarification...
To comment about
Heatran, one must take weather into consideration, for sure. The most common objection, right now, to Heatran, is that forces us to not use Rain, which is exactly what Team 2 wants. I don't really agree on that matter; well, Team 2 can take advantage of us not taking Rain, of course, but it can take advantage even if we take it! Don't forget that doing so will enable them to pick Swift Swimmers, that can have quite a bit of impact on us. Even if they don't do so, they still can run something like SpD Jirachi without fear, since Fire weakness is substantially removed, and can easily check quite a big portion of common rain abusers. Furthermore, their Heatran will be underwhelming, but Celebi can come in on Politoed as it pleases, and spread paralysis on our team, if Thundurus has been previously eliminated/weakened. So, unless we decide to take Politoed as our last pick, Team 2 can still punish us regardless of the choice we do. Thus, I find more valuable to be able to virtually wall/set-up on the entirety of Team 2 right now than to allow us to maybe choose Rain later, and resort to a less effective pick.