Personally, I hope they steer away from the TT racegun stuff. Though perhaps that's wishful thinking considering Taran's role in training I guess. Part of me thinks it would be cool to see some less common stuff. I seem to recall the third one ends with John without all his connections to the Continental etc so perhaps we'll see him geared up with less Gucci stuff. As a big fan of films like Hard Boiled and The Killer etc and the Beretta 92FS, I feel the John Wick franchise could perfectly pay homage to some of the brutal up close and personal gunfights that you see in HK cinema of that era.
Supplement the Beretta M92FS with other guns from the first Max Payne game, M11, sawed off shotgun, Colt M733. Maybe even the M79 and Jackhammer if they're feeling a bit funky. So, with the exception of the M79 and Jackhammer, just more basic stuff that might be able to be sourced from the black market/people still friendly with John but not on the level of the Continental.