At the end of Byleth’s presentation, Sakurai said something along the lines of, “We’re going to continue bringing DLC content down the line. I thought that maybe 1 or 2 might suffice, but...well...” and then 6 additional packs were revealed.
It’s highly likely this is just him saying “surprise! 6 more!” But I think it’s highly plausible that there were originally going to just be a few extras (In my humble opinion, I think it was Steve and Sephiroth at least), but then decided to make it into something more. This allowed them to revisit ARMS and XC2.
I’m probably wrong though. All I’d say is that 3rd parties seem all over the place, while First parties have been consistent with being emblematic of Switch first party software that previously had minimal content or no playable character to directly represent it.
Mii Costumes will dictate quite a bit going forward, I think. If, for example, we get a KOS-MOS Mii with Pyra/Mythra, but don’t get Lloyd...I think that is suspicious enough to suggest he might be coming later. Granted, I expect him to be there personally.
Monster Hunter is also interesting here. If it’s not here with Pyra/Mythra, then it suggests two scenarios: one in which is becomes playable, and one in which a related genre/series from IP holder (Capcom) is the playable pick.
It’s always fun to have implications from a Mii costume reveal in one of these presentations, I’m plenty excited to play the Xeno-gals, but I must admit...with two characters left this has the potential to shake things up.