It's hard to say what the future is. Who knew that San Andreas was going to garner the following it did for the length of time?
Like Charles, I remember the Paruni CS:GO server being probably more popular than the SA:MP server on a fairly regular basis. The whole community kinda dropped off with inactivity over a prolonged length of time.
To be exactly as it was, on Argonath, games like GTA V offer a better opportunity - but the "official" client being offered limits the chance of a third party developer being successful... If we're following the same pattern as GTA SA, then a successful platform would take a single player game and make it MP with free-roam possibility. This suggests games like "Just Cause 3" etc as potential candidates.