More than anything I’d want to have a complete overhaul of the frankly awful character systems into something more varied, impactful and mechanically actually interesting (and closer to CP2020), that allows me to actually roleplay the character instead of just bumbing up his damage and armor in various ways. This encompasses many things from combat, to interactivity, narrative and the minute to minute gameplay. (And of course it will never happen, but it is the #1 thing I would want.)
More interactive and reactive city where doing stuff gets a reaction. Factory yards where I’ve slaughtered the gangers refilling with workers, and some such, NPC’s and traffic reacting to the happenings around them and different social classes having their iwn behaviors, gangs and cops having independent reputations to which your actions factor in (can’t be everyones buddy), and so on... (And obviously this won’t happen either, at least not fully, but it is the #2.)
Alternative narrative lines that allow for more open approach to the main story and include more meat on the lifepaths throughout the game, and perhaps even puff some life into the gangs too and some of the sidemissions and their rippling reactivity. (And that’s the last thing that will not happen, but it is #3.)