And understand, I don't have a problem with moving beyond an established canon; if I did, I wouldn't love TNG, DS9, VOY and ENT, and I wouldn't have read every bloody ST novel (except for a handful of children's novels) ever released.
I'll admit that where M*A*S*H is concerned (and yes, it looks like I'm veering off into left field here, but stay with me), I haven't read the book, or seen more than a few minutes of the movie (I have seen the stage play, however). But it seems to me that it was a case of the television series actually being the best
incarnation of the idea, and actually improved
as it evolved beyond the original material: stereotypical Henry Blake and Frank Burns being replaced with much more believable Sherman Potter and Charles Winchester, Houlihan and Klinger evolving out of their one-joke stereotypes, experimental episodes, Alda vetoing a Hawkeye gag that turned out to be a repeat of one he'd actually done and forgotten about in an earlier season, and so forth. But this was a case, like TNG, DS9, VOY, and ENT (and maybe, maybe,
the Abramsverse), of expanding
on the established canon, not stomping
I have no problem with an Oz movie expanding on what Baum wrote. Or even attempting to answer the questions raised by Baum's own inconsistencies (like the passages in Land,
accusing the Wizard of collaborating with Mombi, to get Ozma out of the way, that are conveniently forgotten two novels later, in Dorothy and the Wizard
). Just as long as they aren't stomping on Baum.