Everyone who's saying Dragonite is next for suspect, don't be stupid. Mence and DNite aren't even remotely similar in the way they're used, apart from the fact they're both dragons with access to DD.
Salamence has massive destructive power due to its higher attack stats and speed, so with just 1 DD it can outspeed pretty much anything without a scarf and hit it hard for good measure, while Dragonite is a bit bulkier, but a hell of a lot slower. Plus Mence has Intimidate which cuts its opponent's attack, so it can weaken physical threats quite efficiently, while Nite just switches in with no helpful ability whatsoever (OK, so Inner Focus makes Scarfrachi slightly less annoying, but apart from that it's pretty much useless). Dragonite also gets a few nice support moves (Light Screen, Heal Bell, T-Wave) so it can run bulkier sets that don't rely on pure sweeping power, while Mence's list of useful moves is mainly composed of attacking moves, which means that pretty much every Mence is designed to destroy as much as possible.
Tbh, even though personally I've never really had a problem with Mence (I've yet to face a good Mence player due to the fact that I don't ladder as often as a lot of you), I can see why it's a suspect, with that raw destructive power and the potential to 2HKO pretty much the entire metagame if used properly.
Now, as for the other changes that Latias's move upwards is gonna cause, my favourite Scizor counter, Zapdos, should be going up in usage without Latias being able to switch in and wall it. People are saying Starmie will be Latias's successor, and that makes sense, seeing as they have similar movepools and typing, although Starmie lacks the bulk of Latias and isn't as powerful. Its speed should help out in the long run though. For this reason, I actually think Scarftar will be more than just a fad, as it counters Starmie just as well as it did Latias.
Obviously, Infernape's free to do as it pleases now, without Latias coming in and sponging all its attacks and ending the fun. I think Blissey might just go down as well, simply because it doesn't need to wall Latias anymore and Infernape can pretty much always OHKO with a Close Combat (hell, even Specially-Based MixApe has a good chance after SR damage is taken into account).