Hi, hi, hi. I have opposing thoughts, Reindeer. I think it is both a film and a series, and quite obviously both, as outlined in an article in filmmaker magazine. It was written like a film and then shot like one, and Lynch himself, a filmmaker, considers it a film, or at least doesn't see a need to make a distinction between film and TV. I do think, in contrast to your previous post, that this is more structurally filmlike than other shows, perhaps more filmlike than any show outside of Top of the Lake. It was written and shot like a film, only broken up later. Parts 1 and 2 function as a movie, parts 3 and 4 also do, and part 5 and 6 could/should have been edited the same way, as should have 7 and 8 in that the final scene of the earlier episode is also the opening scene of the next (7 ends with Cooper and Ray leaving prison and 8 starts with them in the car, moments later; 5 ends with Cooper looking at the statue with Johnny Jewel playing, 6 starts with the same scene and music). The inclusion of musical sequences in the middle of certain parts, such as in Part 5 and Part 8, proves that they're not only there just to bookend a chapter, but to add thematic and emotional resonance. When you watch them all together, the lines between Parts dissolve, and it all feels like one continuous movie that you can pause at any time, whether its at the end of an episode or the middle, and it doesn't matter. And if Berlin Alexanderplatz and the obviously episodic Dekalog are considered movies, then The Return is also a movie.
It's also a TV show, no doubt, since it is broken into chapters and aired on TV on a weekly basis. But it transcends either medium, in my opinion, and that statement doesn't only have to do with quality. I do agree that it opens a can of worms regarding what should be considered a film nowadays, but then again I think plenty of TV has been blurring that distinction, like you said.
Edit: I'd also add, in a controversially converse way, that the addition of musical scenes as punctuation both serves to make the thing a TV show, lending it an episodic element, but also at the same time makes it even more of a movie, in that you can argue that it needed the musical elements to differentiate one episode from the next since they otherwise are hard to tell apart since each opens and closes almost arbitrarily. There's also the pretty obvious element of the musical scenes simply being a more ambitious form of pop music playing over end credits a la Sopranos. As far as why it isn't edited differently for the Blu-ray, perhaps Lynch fell in love with the form that he arrived at and felt no need for further editing. But I'm a guy who's open to even considering the credits to be part of the film, rather than an element of episodic TV. An element similar to onscreen text in a Godard movie, or multiple or late credits sequences in an Apichatpong Weeresthekal film. In other words, I think the TV form has been blown wide open, with Peaks as the final ignition.