Will iCloud Drive accept any type of file?

In theory, yes.

I travel a lot. What I want to do is load 4-5 movies from my iTunes library (really on my NAS) onto iCloud drive when it's released. Then download what movie I want to watch on the plane. When done, delete it from my iOS device so I can download another movie on the return flight.

Will iCloud drive be able to do that?

I'm hearing as others have said; iCloud Drive will accept any file, and sync them between devices...and will still have individual "folders" for apps that already sync with iCloud documents, like Pages, Numbers, Keynote, TextEdit, etc.