Igglybuff Jigglypuff Wigglytuff Azurill(?) Marill Azumarill Gardevoir (I doubt they'd change Ralts and Kirila) Sylveon Furabebe
The Clefairy line seems like a safe bet, would be bonkers if it wasn't, but I also think the Chansey line will be getting the type as well.. I feel Togepi WOULD get it, but they already get a type added later in the line so I'm not so sure..
Snubbull perhaps? (at this point I'm just looking at Pokemon that are pink), maybe Skitty? Probably Audino..
Then I start thinking about all the Pokemon that are not necessarily likely, just semi plausible and would definitely benefit from it like Volbeat/Illumise, the Mareep line, Plusle/Minun, Bellossum, Sunflora, Cherrim seems pretty possible.. Chimecho, Musharna, the Reuniclus line perhaps, Milotic? Luvdisc? There are at least definitely a couple of possibilities. I just feel like they have to add it to a couple of 'substantial' Pokemon considering the likelihood of there being a Fairy type Gym leader or Elite Four member is pretty high.