The problem with doing the whole "would I use it" test is that everyone would use different things. Some people would use things that other people would call simply unviable. There should be some line, but rankings are extremely subjective. When looking at a Pokemon like Salamence, you have to wonder what niche it has. I personally see a tiny tiny tiny one; a Dragon Dancer that gets stronger as time goes on. However, the loss of defensive utility when compared to Dragonite and the loss in power and dual STAB when compared to Mega Charizard-X makes it never really worth using. Should we rank it because it has a tiny niche and can do something, or should we not rank it to make sure we don't advocate using it? Vaporeon isn't ranked, for the same reason, in my opinion, Salamence shouldn't be ranked. I'd compare Blissey to Salamence too; both have a tiny niche but are rarely, if ever, seriously worth using. I know the thread kinda exploded the last time Blissey was mentioned; but come on. Its niche is so small that it really shouldn't be thought of as on the same level as Magnezone, who has no competition for its role. It's a very solid Pokemon with solid stats and a solid level of effectiveness; its problem is that its niche isn't that necessary. It's the perfect C rank, in my opinion.
Perhaps you could argue that Blissey's niche of taking less hazard/weather damage as big as Magnezone's niche of trapping Scizor, Skarmory, and Ferrothorn for different offensive Pokemon, but I'd entirely disagree. I agree with someone's proposal earlier that we should possibly change the definitions, and definitely move some Pokemon around to reflect their actual viability. Every Pokemon is usable, but only those with distinct niches in OU should be ranked, again in my opinion. If something has a distinct niche, but it doesn't perform as consistently as desired, or the niche isn't that important, it should be D rank. Then again, there are some Pokemon no one really knows what to do with, like Meloetta, that are actually really fun to use. SubCM and Assault Vest are interesting sets that are unique in OU, and I won't stop using them if it gets unranked. But I'm not sure if something with no defining niche deserves a rank, unless there's a precedent for that.
If we want to continue the "would I use it" test; here's mine. These are the Pokemon I'd never use: Alakazam (non mega), Blastoise, Espeon, Haxorus, Hydreigon, Sharpedo, Smeargle, Zygarde, Blissey, Escavalier, Goodra, Houndoom, Salamence, Tangrowth, Tornadus, Umbreon, Dugtrio, Hawlucha, Kyurem, Mantine, Roserade, Abomasnow, Cloyster, Cofagrigus, Empoleon, Jirachi, Snorlax, and Toxicroak.
That doesn't mean that those all should be removed, as obviously I cannot speak for everyone. But I can say, like in many viability threads, the lower ranks are still inflated.