Hmm, you know, many are speculating that Sirfetch'd, among other things, may be a remade version of a possible scrapped evolution for Farfetch'd in the Gold & Silver beta. If GF are remaking the scrapped GS Beta Pokemon, then maybe that's where we should look for a possible counterpart. That automatically knocks us down to Gen I & II Pokemon. I'm going to remove the Legendaries and ones who have Mega Evolution as I'm still hoping those get used as Gigantamax so would be strange for them to get a new evolution. That leaves Tauros, Lapras, Ditto, Unown, Girafairg, Dunsparce, Qwilfish, Shuckle, Corsola, Delibird, Skarmory, Stantler, Smeargle, & Miltank.
Now already I know what some of you are thinking: DUNSPARCE! Or
Yung Dramps (and I know one other Youtuber) would love Delibird one. The leak did mention a Lapras Gigantamax, could they have mistaken it for a Galarian Forme or evolution? Well, remember I'm looking for a Pokemon which had a scrapped evolution in the GS Demo. Fun Fact, this would mean Ditto and Qwilfish (which evo looked to have then been made into Whiscash). HOWEVER there is one other Pokemon here which had an interesting beta design: Girafarig. Originally it really was a symmetrical Pokemon, except its back black head has a sinister expression and I believe it was Dark/Normal (it even had a pre-evolution but that's not important). Now what if they brought back this idea but as an evolution AND instead of Normal/Psychic they made it Normal/Ghost! Why Normal/Ghost? Well I'm assuming the developed head is the Normal-type and the undeveloped tail-head is the Psychic. If they're remaking the GS beta design then the tail-head would change into a full developed head thus would be the one to get the Type change.
So, yeah, that's my guess. Girafarig will be the Shield counterpart (Girafgira?) and become Normal/Ghost so it could be Alister's ace like Sirfetch'd is being predicted to become Bea's.