Also over the last few years I've hit multiple schema-migration bugs that only occur on relations spanning apps, and no such bugs within single apps, so there's definitely a "less well-trodden path" argument against multiple apps.
Finally migration squashing didn't work well when I tried it on my multiple-app project; it wasn't able to squash past the first foreign key to another app. This might have improved in the last couple releases.
I've not worked on a project as large as the one you describe, so I'm open to the possibility that at that scale there are new problems that crop up (e.g. managing a single migrations directory could be fun with that many developers), but I'd guess that most developers won't hit that scale, and yet the common wisdom for getting started is to try to split out small apps early, which I consider harmful.
Agreed - I would note that there is nothing stopping you from having good structure (with multiple independent/encapsulated services/apps) inside a single Django "app" (as the OP suggests).