I just thought of a point that isn't for Lillie or the new people, but for the trial captains.
With Kahili doing the Flying Z-move in that trailer and Ryuki showing up, I'm confident that trials are returning, but at least one or two captains are being replaced with either Kahili, Ryuki or both.
Since there is what looks like a golf course on Akala Island, I'd say it's just about a definite that Kahili would be a new trial captain on Akala, probably replacing one of the Akala captains. Thing is, every Akala captain from SM has a motive to drop their role - Mallow has to run her cafe, Lana has sisters to look after and Kiawe has a dancing goal to follow. I couldn't really say which one of them would probably be replaced, but I'd assume the captain that does get replaced would either show up for a different purpose outside of battle or become an Elite Four member.
As for Ryuki, it is of course possible that he doesn't become a captain, but the Dragon trial in SM plus Kommo-o's exclusive Z-move suggest to me that the trial will hold a little more for us this time, possibly with even a new captain. Since Mina never actually ran a trial in SM I don't think she'd be replaced whatsoever, so one of the trials on a different island would probably be removed so that there could be a Dragon trial on Poni and a Fairy trial on either Poni too or elsewhere. I'd be confident in saying that the Ghost trial could be removed if Acerola decides to keep her role as an Elite Four member this time around, but I don't think the Fairy trial would be on Ula Ula. Instead, I'd set the Fairy trial on Melemele Island, possibly in Melemele Meadow or somewhere near - especially since it's a place involving flowers, something Mina mentioned as a part of what she wanted for her trial, the signature location of Cutiefly aka one of the poster Fairy types for this generation and possibly Mina's signature Pokemon, and the same Island as where Ilima does his trial, with Ilima being a confirmed friend of Mina. I know that in one of the pre-release screenshots we have the same Melemele Meadow scene with Lillie, but the Meadow could still be expanded upon in USUM to contain a trial area. Plus, the other meadows of the region don't make much sense as trial places to me - Akala doesn't have a meadow (plus it already has three trials), Ula Ula's meadow leads to the Lake of the Moone/Sunne which seems way too close to an important area (I know the SM Dragon trial was next to the Altar but I wouldn't imagine the Fairy trial to be the final one) and the Poni Meadow leads to Resolution Cave, which seems like just an odd place to put a trial - especially when the cave is laid out as though a legendary could be encountered there. Plus, the Melemele Meadow leads to that cave I've forgotten the name of, which in turn leads to Kala'e Bay. It'd be nice to see that Cave and Bay used as part of a fairy trial - maybe the cave is full of flowers now and Kala'e Bay has a small platform where you encounter the trial Pokemon.
Oooor maybe the Fairy trial just is the ghost trial with Mimikyu remaining as the totem, but the trial itself is more Fairy-themed than Ghost-themed. Idk, I'm just rambling at this point.