Stay with me here guys.
The point of Arnold being in the film is "legitimacty". As I stated before. Arnold LOL'd at Rodriguez, wanting to "lead" a pack of Preds'. Campy, comic book fodder save that for a different realm of entertainment (books, comics, video games etc...).
Which is the entire point. Arnold would have never done AVP's and even LOL'd at Preds (the superior movie of the bunch) because he knew it was crap. Hence putting him in it, would still be crap (as pointed out).
Him holding out AND at this point in his career (money is in the bank, Star is on the map) he can be selective. So by virtue of him merely meeting with Shane Black (and I'm gonna say Black has a LEGIT non Comic-Book script ala the first pred) Arnold is already in the process of legitimizing this thing.
If Arnold agrees. You can count on a good Pred (finally) movie.