I felt the same way about the lack of Malia! I'm kind of torn over the main 6A storyline, too-- I feel like if we have to do the whole "Stiles is being pulled from our existence!" thing, then it would be a perfect time to explore the relationships between Stiles and the Sheriff, Scott, Melissa, and the pack, who are all basically his family. Obviously, Stiles and Lydia are best friends, so that includes her as well, but if the majority of the focus is going to just be on just those two in a romantic sense, I'm going to be disappointed, to be honest.
I'm also a little bummed about the lack of Parrish! I'm hoping it's because they don't want to spoil too much about his storyline, since he's possessed by a Hellhound and they're supposed to be associated with the Wild Hunt and the Ghost Riders. Maybe they're gonna want Cerberus back?
So, yeah, I admit, these trailers have me a liiiiittle hesitant for Season 6, but I feel like this is the case every season and it ends up being fine in the end, lollll. Jeff loves to make trailers that give you a taste of what's to come but that don't truly reflect the full scope of the season, so I have a feeling our reservations will end up lessening or disappearing once we actually see the extent of what is actually going on. There's 20 whole episodes again this season so that should be plenty of time for our faves to have their moments, haha. ;)
Anyway, in terms of theories, I am wondering if maybe Stiles being erased from everyone's memories is why we end up seeing full-coyote Malia? Since he was so crucial in helping her learn control over her powers, maybe without the memories of his help (plus the boost from stealing her mom's werecoyote powers), she's going to have trouble controlling her shifts? We really didn't see much of anyone else except for Stiles, Lydia, Peter, and a little bit of Sheriff Stilinski, so I have a hard time coming up with theories as to what's up with the others like Scott, Mason, Corey, Liam, Hayden, etc. yet.