I've watched a couple movies on this list, courtesy of Netflicks. I've got a quibble. I think there's this notion that unconventional=interstitial. There's nothing interstitial about "Oldboy", for instance. That was straight-up psychological thriller. Though it had a few interesting camera tricks, that does not equal "interstitial". There was no blend of genres, or feeling of strangeness as one realized one was spinning beyond the norms of film genre boundaries.
"La Jetee", for instance, married highest of the high, art house, cine-style with very low B-movie science fiction.
Terry Gilliam's movie "The Adventures of Baron Munchausen" is not interstitial at all, nor is "Time Bandits". They're fantasy.
"The New World" is just a very stylized - and f-ing wonderful - historical romance.
"The Pillow Book", I think, is also not quite Interstitial, just really f-ed up Erotica.
Is oddity enough to make something in-between? I don't think so.
The only movie mentioned that I have seen so far, which I would agree is "Interstitial", is Dali Destino.
I think it's very easy to say something I like that is not like a Hollywood movie is interstitial, without a clearer sense of what "Interstitial" really means to the cinema.
Who wants to try coming up with a better definition of "Interstitial" for the purposes of film?