Without the Choice Scarf, many setup sweeper will be a pain to deal with, like Dragonite, Gyarados or even Tyranitar. Most people will use lure such as Shuca Berry Jirachi, Empoleon for exemple to revenge kill Dragonite (unless its an Yache Berry variant but you will have most of time a decent shot to beat it). Without Scarf Tyranitar/Scizor, Starmie would be even more effective in the metagame since it will very hard to pursuit without an Weavile (which doesn't have the required bulk to switch in an Hydro Pump + SR with some prior damage), spinblocking would be really hard since without the Choice Scarf, Rotom-A can't be used as the best spinblocker to it since the defensive variant is 2HKO'd with SR and prior damage and Gengar isn't really the best switch-in to Starmie. Balanced/Stall team would have problem with Gengar without Scarf Tyranitar, you will have to rely on Skarmory and pivoting to beat it. Of course, U-turn would be less used since it will loose many advantages (Scooting or for exemple, CB Azelf u-turning on an Tyranitar switch-in and than pressuring him back with Scarf u-turner which outspeed all Ttar variant).
Without the Choice Band, many mon will loose their ability to being really good wallbreaker like CB Ttar which, even if rarely seen these time is still doing an huge work and is still a huge team for every team (even prepared one), Infernape doesn't suffer to much from this change but it will be not used as lead scooter anymore, Flygon with the lost of both of Choice Scarf and Choice Band would be an very bad lead, Scizor will obviously suffer a little bit with these change due to the lack of power of Bullet Punch which is one of his main advantage : having one of the best priority in the game and using it to revenge/finish an mon.
The best users of Choice Specs are Electric types such as Zapdos and Jolteon and they will still have many other good way to deal damage (better than the Specs one like LO or Magnet), SpecsPert is rare but i'm not seeing him suffering from this change, SpecsRachi is fun because Doom Desire is broken since it have literally no stab which mean you can spam it everytime in the game without worry about an Tyranitar, Trick on Lead Starmie would be like non-existant,
As Aerodactyl Legend said it, Dugtrio would don't have to play an Focus Sash or an random Scarf to be sure to revenge kill/trapkill Heatran.