With the characters!? You use the familiar characters to set the sceneria. Like they say a picture tells 1000 words. The moment you show Arnold/Dutch, Agent Garber you instantly connect people back to set the film in the right direction. Predator 2 already sets the movie forward 10 yrs. This one will take care of those other 20 yrs in between.
It's pretty safe to say that unless they are going to use the films as a reference, it really doesn't matter. Now setting the film before Predators and after Predator 2 does somewhat insinuate there may be a reference or tie into the other films! That would be awesome if they were connected somehow, odviously it would refer to Predator, maybe the CIA team from Predator 2 under the leadership of Agent Garber and then show Arnold turning down a job and recommending Royce because he will cross the line Dutch would not and Royce upon completing his task and being taken. Or at least show someone mentioning Royce completing his task and gone missing. At the end of the credits they should show Liam Nesson contacting the Beserker Predator via Rouces' walkie talkie and doing his famous lines i.e. I have a particular set of skills..... I will find you, and I will kill you!! BAM!! I just wrote the movie!!