Hey Bribery!
I absolutely love this team--and it's a great example of the increasing popularity of Gothitelle-Trap-Sweep teams. Also,
not being biased or anything, but that SubSalac Terrakion is totally cool! I was reading over this RMT last night to formulate a rate today, but I couldn't exactly come up with any major threats that you couldn't play around, so I decided to give the team a try. I looked out for things that really hurt the potential of the team, and like everyone else said:
Lati@s. However, I found something else to be a big pain in the buttocks--
Venusaur. Although you do have sand to stop its sweep, Hippodown doesn't exactly appreciate switching into a LO Giga Drain. So I found myself forced into awkward switching (like Genesect to Hippo and back to Genesect to get sand up + outspeed), which ended up with unnecessary hazard damage and possible prediction. Venusaur is able to get a free Growth on Gothitelle locked into Tbolt, +0 Terrakion, Latias, Rotom-W, and Genesect locked into Tbolt; and from there could OHKO basically any Pokemon on the team. The best bet to taking it out is to sack something and then bring in a full HP Gothitelle, but if something happens to Gothitelle that would be unavoidable, Venusaur is very difficult to deal with. I'll try to cover both problems in 1 Pokemon so I don't ruin the synergy of the team: Heatran. Not any Heatran, though. It's basically a Specially Defensive RestTalk Heatran with Shed Shell, and was able to honestly 6-0 GeneSun teams back when Lavos's team was posted. It deals with offensive Sun teams extremely well and walls most Venusaur to hell and back. If said Venusaur has EQ, though, Latias deals with it. If they have EQ + HP Ice, Genesect deals with it. If it's the Standard Growth Sweeper (Growth/Giga Drain/HP Fire/Sludge Bomb), Heatran deals with it. EVEN IF IT HAS SLEEP POWDER, Heatran deals with it. Sorry, I'm getting a bit excited, lmao. With Heatran, Venusaur would be a non-issue to your team. That's not all, though. It also deals with the Lati twins, as it can switch into Draco Meteors galore, Roar out CM Latias for Genesect to deal with it, and provide a cushion for Tornadus-T. And that being said, I feel that
replacing Rotom-W for this Heatran would be the most logical option. Although Rotom-W is a very good check to many rain teams, Latias is even better (which we're going to tweak in the next paragraph). Here's the set:
Heatran

(M) @ Shed Shell
Trait: Flash Fire
EVs: 252 HP / 248 SDef / 8 Spd
Calm Nature (+SDef, -Atk)
- Lava Plume
- Roar
- Rest
- Sleep Talk
I'm a bit paranoid when it comes to EVs. I like to speed creep Heatran speed creepers, lol. That's what the 8 Spe EVs are for. The rest of the EVs supply the most special bulk possible. Shed Shell to escape the clutches of Dugtrio, making GeneSun extremely easy to deal with. RestTalk gives your team undeniably useful sleep fodder for Pokemon like Breloom and Amoonguss, and sometimes nab some nasty KOs with unsuspecting Sleep Talks.
Anyway, on to Latias. SubCM Latias is definitely an efficient sweeper, but I feel like
Psyshock would be more useful over Substitute (for this team, at least). Psyshock allows you to hit Breloom much harder (which can do some MASSIVE damage if it's Jolly, since Gothitelle is OHKO'd by a +2 Bullet Seed), Terrakion in your sand (dang that Sp. Def boost!), CM Keldeo (has the potential to 6-0), Tentacruel (Hippo, Gothitelle, and SubCM Terrakion don't like Toxic Spikes), and Gengar (risking the Speed tie is worth killing a massive threat). It also hits a plethora of other Pokemon, but those listed are the majors (and reasonably large threats to your team). This is also a more solid check to Keldeo, meaning the loss of Rotom-W as a secondary Rain-check is a bit softer. Heatran also checks Volcarona, which would otherwise be a big threat once Rotom-W left. And so, with that, I finish. I hope these changes can benefit you! Good luck! :]
Summary of Changes
: change to 
: Substitute → Psyshock