Due to largely overlapping vocabulary and morphology, mutual intelligibility among the three Scandinavian languages is near-complete (and in spite of claims that “Danish is impossible to understand”, this is largely a matter of hyperbole and changing mores – even after the most drastic Danish phonetic changes occurred in the early–mid 20th century, participants at pan-Scandinavian events continued to each speak in their own language for decades).
Now, this situation is broadly comparable to the situation between the Bosnian/Croatian/Montengrin/Serbian languages, and for BCMS, there does exist an approach of trying to teach all four languages at once in a single programme. For example, in Alexander & Elias-Bursać’s BCMS textbook, dialogues and reading passages could be in any one of those four varieties, with commentary explaining how that variety differs from the others. My question is whether a textbook has been published, in any language, or a university course offered in which Danish/Norwegian/Swedish are all tackled at once.