Next gen consoles are more similar to PC so they will be easier to work with. Now it depends mostly on the engine choice. It could be that Rockstar will just update RAGE or maybe develop a completely new engine.
If they stay with RAGE then they already know the engine and won't have problems making a good game with plenty of content. If they make a new engine they may have to either delay the game while working on other titles trough which they will perfect the engine, or make a game with less polished feature.
Either way, IV was a HUGE step forward from SA. There will NEVER be another step as huge as that one was. The graphics will have more polygons and more shaders.. but the jump won't be nowhere near what they did between SA and IV. Then there were animation updates with them using Euphoria for the first time in IV and it gave them a lot of problems. Now they know how it all works and won't have those problems either.
All in all, I would expect the next GTA to be pretty similar to V and even if it does take away a few things, I think it will have a whole bunch of features to be more fun than IV was.
I don't think IV was that big of a step up from San Andreas...
Still a game where you steal cars and shoot people except with added physics, car damage modeling and boring mini games like bowling replacing crime simulation like Burglary
I was talking about the technical side, not the gameplay. The basic gameplay has barely changed anything since GTA I. The gaphics, physics, animations, cover system, driving, interaction with the world, pedestrians... all of that was technically much improved from SA to IV and I'm saying we won't see that kind of a big jump ever again.
Actually this isn't completely true. There is Mafia II, which IMO has one of the most immersive story line, deepest rpg, and most historically accurate open world crime game to date. Had Mafia 2 added all the content that came with DLC like Joe's Adventures and Jimmy's Vendetta, added more sandbox variety side missions/random events around the map, then Mafia II would have definitely rivaled GTA IV in terms of game play.
Mafia games were both great, but they never knew how to make proper free roam. In those games you get into the story, complete it, and then there's nothing left. I kind of consider them linear games set in an open world as there is nothing to make you want go in and just roam the world. That is their major flaw.