I don't think there will ever be a 3SR. Reasons being:

>pathfinder already exists
Like it or not, a lot of people went to PF 1e. That WAS the 3SR. It's not the same game, but it was close enough for those people.
>people don't want a "system" anymore
5e has different rules for PCs and NPCs. Drove me nuts at first, but I eventually accepted it. 3.5 was the last edition to have a truly coherent "system" for handling both players and monsters. You could add cleric levels to a minotaur and suddenly he was a whole new challenge. Add a prestige class to a rakshasa and make him something unexpected. But now, you can still do that, there's just no framework for it in the rules: you just make it up and tack on whatever you want, and figure out its challenge rating afterward. That's okay too but that was the closest there was to a "design philosophy" in 3.5e.
>too complicated
No one is pining for a separate BaB, skill points, and save progression system, when proficiency exists and it was an easy way to wrap everything together. That's not to say a revised 3.5e couldn't have a 1/2 level progression like 4e, or something akin to 5e proficiency where everything's on a unified track for the most part. But that, plus complicated subsystems for everything, makes it harder and harder for new players to learn.
>most 3.5 content isn't OGL
This is a big one, a lot of what made 3.5 great was the insane number of classes an feats and prestige classes and monsters. But most of them outside of core aren't OGL. Can't use any of that stuff. You can make your own, and something like Arcana Unearthed that's an entire alternate player's handbook is really cool, but unless everyone rallies around someone's OGL-dodging 3.5e retroclone with a ton of extra content, it's not happening

That said I still love 3.5 and if anyone wants to listen to an autist droning on about old 3.5 material I do it on youtube sometimes: https://www.youtube.com/watch?v=0wqL3S6cTes