Yeah I'm going to have to agree that Weavile should stay in A-Rank. Ice / Dark has nice coverage, yeah, and Weavile can definitely sweep significant portions of the metagame, no doubt. But Weavile does not have the strongest of attacks and needs LO and/or SD to be a threat. As RabidChipmunk said, Weavile has a really bad case of 4-moveslot-syndrome. Weavile really wants SD, as well as both Ice Shard and Ice Punch, plus both Night Slash and Pursuit. It also needs Low Kick to deal with the steel. Weavile is also really frail and thus struggles getting the boost. I believe it is not S-Rank material; it doesn't define the meta like Raikou and Mienshao do. Thus, Weavile should stay in A-Rank.
I agree with moving Mew down to A-Rank. Mew is definitely a great Pokemon and a versatile one too. However, here's the thing: It isn't amazing enough at anything it does to warrant S-Rank. 100 stats across the board aren't exactly spectacular, and while Mew is unpredictable, its typing is rather alright at best. NP set seems cool, but tbh I think Azelf does that better because of his better offenses, greater Speed tier, and Fire Blast being more fearsome to things like Bronzong and Registeel. Again, SD is threatening, but its not the most threatening SD sweeper. Mew has a shit ton of tricks up its sleeve, and its versatility and greatness warrant top A-Rank for sure, but it's not exceptional at anything it does, nor does it define the metagame. I'd say Mew for A-Rank.
Regarding Togekiss, I'm torn. One thing's certain that Togekiss is definitely a bitch to face, and if it gets a T-Wave, it's annoyance time. Togekiss also has great bulk to boot and can take quite some hits, so it can spam T-Wave+Air Slash with ease. NP+Heal Bell Togekiss is a solid stallbreaker, and Stall teams absolutely hate its presence (as with Crobat as well). It is a great Pokemon and also, HustleKiss is possible for surprise factor. Its Speed and SR weakness are a bit noteworthy though. I could see Togekiss as either S or A, leaning a bit towards S-Rank though.
I feel at this point that Qwilfish should be B-Rank. Qwilfish does really well in the current metagame, he's an excellent Spiker, and he's also a great check to things like Mienshao, Heracross, and Victini (plus Escavalier). Qwilfish does the job of Spiking pretty well, and T-Wave, Taunt, and Haze are all cool support options that can fit certain teams. Raikou and Zapdos demolish it, sure, but that's why you have teammates, right? Even if Qwilfish doesn't have much use outside of its niche, it has a very good niche. Being able to check some dangerous threats in the metagame, setting up Spikes, and pulling off random support options are all good reasons to use Qwilfish in UU. Qwilfish for B-Rank.
*continues Amoonguss for B rant*