I think getting caught up on what does and does not make the most sense from a business perspective is a bad way to go about speculation, seeing how that doesn't really line up with what we've seen previously.
While characters like Bayonetta, Joker, and Terry are cool, they aren't these massive names that make casual players' jaws drop and say "Holy ****! They added him to the game!? I've gotta buy the DLC now!". As I mentioned in my Banjo post, Nintendo could've went "Sorry, but we'd rather have Master Chief or Steve in the game. They'd be more profitable for both of us". There's no guarantee Microsoft would've went along, but the fact that Banjo was still the first character brought up in negotiations shows that making the most money is not the key to Smash's DLC.
I'm sure the accountants have some say in who gets added, but I don't think it really has any impact. Smash characters are gonna make money because they're Smash characters. Nintendo had confidence that Corrin would sell in 2016, despite his DLC releasing before Fates did internationally. As such, saying to ourselves "X is cool, but is it what would interest Nintendo as a corporation?" seems to be a wrong step.
Well, I do think Nintendo has a tendency to choose characters that they'll ultimately profit from, and when I say "profit", I don't necessarily mean just the sales of the DLC.
Just a while back, we saw Atlus having people participate in a poll that asked them which of their games people would be interested seeing ported to the Switch. Doesn't surprise me that Nintendo is trying to slowly shift Persona away from being a PS4 exclusive.
Dragon Quest has a long history with Nintendo, but it's not exclusive to them. They really value that franchise. Seeing how a special DQXI port was coming to the Switch with new features, it wouldn't hurt them to give people another reason to associate DQ with Nintendo. It also benefits SE too, which might make them want to collaborate in other ways.
Banjo is obviously just fan service, but Nintendo and Microsoft are on good terms. Between Minecraft, Cuphead, and this, it seems like Nintendo sees Microsoft as a valuable resource. Best to keep that relationship intact.
Terry's inclusion is the most confusing. Part of me thinks that this is a character Sakurai himself wanted and Nintendo allowed it, but I suppose they could genuinely be interested in the old NEO GEO franchises. King of Fighters XV is coming out soon, so maybe Nintendo is hoping Terry will convince more people to buy a potential Switch version?
Byleth is self-explanatory. Don't think I need to explain.
Again, ARMS is self-explanatory. New IP that they want to keep on the table, possibly because they have plans for it.