What would the plot be?
1) Billy and Taggart go to Detroit and they are the fish-out-of-water? Cue lots of driving sequences where Billy and Taggart drop their collective mouthes whilst being driven through the burnt out streets of the once regal Motor City.
2) Axel, Billy, Taggart are all fired by a failed narcotics bust, and then they go 'rogue'.
3) Axel Foley and the Internet flame wars! Axel, Billy and Taggart are all fish-out-of-water when they are recruited by the Internet department to take out a group of hackers that is raiding personal ID information from Facebook, ning, youtube, twitter or whatever web2.0 app is popular these days....
4) Eddie Murphy decides to make a movie full of in-jokes about himself and his past movies. Includes scenes where he has to go undercover as a fat man as a fat woman inside a fat family - to arrest them for deadily human methane releases; later, Murphy orders himself Waffles whilst at some hotel.
5) Axel Foley finRAB out who shot Uncle Dave, from Beverly Hills Cop III.
6) Surge returns to become the Beverly Hills Cop when Axel Foley goes evil, only to blow his deep-deep-DEEP cover as a double agent who is playing a double-agent... cue Surge quipping "So you're a ... *counts on fingers* triple agent?"
Or... maybe not.