How will the change gang option work ? Will the progress be reset for each gang when you switch so that you can play every gang with one save or is something else planned ?
Nope. See, The way this seems to be going is that each gang will have parallelal events, for example (all of them hypothetical):
Big heist: you invade some place and steal some item, place and item varying with the mafia
Traitor: you find that one of the members of that particular mafia is a spy
Promotion: your promotion is celebrated differently in each mafia, the dragunov would give you some nig gun, the gentlemen would throw 4 prostitutes at you
The thing is, when you change mafia, the save's variables and switchs will be changed to say that you completed the
past events in the mafia that you're changing to, then from that point
onwards you'll see the events in the new mafia.
Id you want to see all the possible events, then yeah, you gotta play 4 times.