The licensing issue is a big deal. Today, so many folks have full or partial ownership of their original "brands" and even their likenesses and voices come into play. It's a way of continuing to generate money for all of the actors, estates and agents who created those original brands. And they have the right to, no question.
So, at the pace that remakes happen, one possible path of least resistance is to focus on the non-licensed original titles that are always hot in the re-sale market and would do well on location. In the Poll thread here on Pinside, they list a handful of titles, (Like TOTAN, TOM, etc) where they wouldn't have to ask for anyone's permission (or pay any fees) above the intellectual property already available through PPS. And a few other 'holy grail' machines will sure fit on that list (i.e. Funhouse)
I am thinking the pinball remake business is hard enough, and the development times are long enough, that a simpler path forward is to just remake the titles that folks would love to get their hands on, and would likely do great on location/routes. And as we are seeing with CCr, existing owners with original machines are seeing their value remain solid, with or without the remakes.