Yeah, I agree. Josh reacted to the Joker trailer in a tweet saying he found this sort of approach better than the "embodiment of chaos" he's portrayed as in The Dark Knight and I strongly disagree because of what you say above - the uncertainty might make the character less of a character, but it also makes him more effective and interesting as an element of its respective film. It also frees the character from the constraints of being his own singular crazy and act more as a symbol or part of a myth instead, to go back to what you were discussing relating to Tolkien and the likes. It reminds me somewhat of the overwhelming tendency there is today amidst audiences to desire for the rational explanation even when there is no need of one that Lindsay Ellis talks about and mocks in the likes of the following:
So probably I spoke too soon about not having any problems with the conceit itself. 😄 That said, appealing to that setting and character's iconography to tell this Falling Down story in a day and age where radical sentiments and hate crimes seem to be on the rise and where these franchises are such a major part of the cultural mainstream could yield interesting results, though as you put it, the bigger concern is how, the "tad soapy" was a cheeky understatement on my part, and given both what we've seen so far as well as the director's track record and so on, I'm not particularly confident.