Pokemon that will love this meta: Anything that has a godawful type combo (Exception: if by 'godawful' you mean 'overly vulnerable to Stealth Rock', sorry, you're still screwed), anything with notable off-STAB moves (Victini's powerful Electric moves), any Prankster (Changes its type before you do), anything with an Ability that fits poorly to its type (All those Electric types immune to Electric and Water types immune to Water), Special attackers in general can use Hidden Power as defensive coverage ("Alakazam became Steel type!" or "Jolteon became Flying type!"), anything that has weather-abuse moves but a sub-optimal typing for STAB-abusing weather.
Pokemon that will hate this meta: Anything with a fantastic or above-average type combo (Fairy/Steel has none of Fairy's weaknesses, Electric/Flying skips out entirely on Electric's one weakness if no Gravity/Smack Down/etc comes into play, and so on), anything that relies primarily on its powerful STABs in the first place (Fire/Fighting can use other types to its benefit, but does most of the work on its own), anything whose type combo goes particularly smoothly with its Ability (Eelektross), walls in general, slow Pokemon in general, and Greninja.
Specific examples include...
-Kyurem-Black, if it doesn't get banned. Dragon/Ice is painful defensively, but who cares now! Its lack of a proper physical Ice STAB is now completely ignorable: laugh maniacally at turning into an Electric type while using STAB Fusion Bolt. Hurrah!
-Most Normal types. All those Normal types with fantastic coverage but, you know, they're Normal? Yeah, now they can be pretty much anything they want at full power and completely ignore being Normal.
-Malamar suddenly gets STAB on Superpower and can completely ignore how horrible Dark/Psychic actually is as a type combo.
-Tyrantrum suddenly get full benefit from Strong Jaw: instead of having to choose between either using STAB or using Strong Jaw (Which is basically STAB on specific moves) it gets both at the same time!
-Gliscor can now wall you like crazy because it can escape that double Ice weakness. Gliscor already often runs Protect just to avoid Knock Off and buy itself healing time, and now it becomes a Normal type in the process!
-Groudon can finally get both STAB and weather abuse at the same time!
-In general many Fire types with Solarbeam love the Sun abuse potential: not only are they getting STAB, but 2 of the three things Grass is good against is stuff Grass resists but Fire is vulnerable to. (Ground, Rock, Water) The remaining one is still super effective on Fire, so it's a great switch to pull. Watch out for Mega Charizard Y.
-Hitmonchan's flexible set of elemental punches is actually maybe usable.
-Gyarados no longer cares that it lacks a real Flying STAB and its Mega form lacks a good Dark STAB!
-Suddenly Clawitzer and Mega Blastoise get STAB on all their Mega Launcher boosted moves. Holy crap. Dragon Pulse in particular renders them resistant to their usual weaknesses: switch in something with Electric or Grass moves and they may have rendered themselves resistant while you switched!
-Mega Heracross' off-STAB Skill Link moves (Bullet Seed and Rock Blast) are off-STAB no longer! Also it can escape that terrible double Flying weakness.
-Fear Porygon-Z's coverage and stuff.
Something worth noting is that there is absolutely no need to pay attention to STAB. That is, if Psychic isn't adding coverage to Alakazam's set, drop it! Since everything gets STAB automatically, there's no reason to care about what STABs a Pokemon normally gets. Dragons can ignore their Dragon STABs if they feel they're not adding anything, Poison can ignore their Poison STAB, etc. This means any Pokemon who has one or more STAB moves it only uses because they're STAB and therefore its best bet on neutral targets can drop the entire concept in favor of something actually useful.
Another point worth noting is that Steel move access is a lot more valuable for switching to the defensively amazing Steel type. Bullet Punch especially can be used as a 'I wanna be Steel NOW' button.
Poisoning, Paralyzing, and Burning are in weird positions: no Pokemon can just assume it's immune like it normally would (Barring Abilities that provide immunity), but lots of them can potentially become immune on an expected attempt via move usage. Two Pokemon both use Toxic, and the one that goes second cries. Keep in mind: type-based immunities do not cure status effects after the fact, only Ability-based immunities do that. If you're hit by Toxic and then become a Steel or Poison type, you're still afflicted with Toxic.
Something to note is that any type that you can be immune to through typing is vastly less appealing than normal, because not only can the opponent switch in a relevant Pokemon if they have one, but they can potentially 'dodge' the move by using a move of the type immune to that move. Particularly relevant is those types with priority: Normal with Quick Attack and Feint and Extreme Speed to dodge Ghost moves, Ghost with Shadow Sneak to dodge Normal and Fighting moves, Fairy with Baby Doll Eyes for dodging Dragon moves while screwing up their Attack stat, Sucker Punch for dodging Psychic moves (I don't yet know if you change type if it fails, but it's sort of irrelevant since that would mean they weren't using a move being Dark would render you immune to anyway), Bullet Punch for dodging Poison moves... you can even use Snatch as another 'dodge Psychic' move and or Endure as another 'dodge Ghost' move! Too bad no priority Grass move exists to give Spore immunity.
Entrapment Abilities are a lot weaker. Anything with a Ghost move can escape even Shadow Tag, anything with a Flying move can escape Arena Trap, and anything at all can escape Magnet Pull by just not using a Steel move.
The type-changing moves and Abilities are pretty useless now too. Camouflage was never amazing, but now it's just redundant.
Synchronoise is now completely useless instead of mostly useless, since anything it affects is resistant full stop.
Sandstorm and Hail are even less appealing then normal if you don't have Ability-based immunity because you can't count on being immune to your own weather. This is particularly painful for the setters. Not only that, but in Sandstorm's case tons of opponents can potentially take advantage of the Special Defense boost spontaneously.
Something worth noting: Adaptability boosts everything you do.