My thoughts have been mostly summed up by the others. As time goes on we'll likely see the armour, the augs, the A.I interface and the other improvements associated with Spartans become more and more mainstream. First we'll see it in other branches, god knows ONI probably wants a few SIVs of their own that answer to them and not the Spartan branch, if that's not already the case. Then maybe Insurrectionists and others outside the UNSC will start making their own super humans as the development process becomes more refined, simplified and mainstream and therefore more easily stolen and reproduced, it's not like they haven't already been trying. After that we could start seeing the improvements becoming more and more easily and legally acquired by emergency services and then civilians. As time goes on from there we'll see more variation and specialization in the upgrades.
Pilots, doctors, teachers, law enforcement, whatever it is you do, the technology that descended from the Spartans can make you do it better. Next thing you know we could end up looking like the Forerunners with the augs becoming a rite of passage for the young, the armour is like a phone and you're expected to have one in some form, human children are basically raised and educated by the A.I they carry and the specialization becomes so ingrained in our society that your specialization becomes the basis of your cultural heritage. To bring another thought to the table though. As the concept of the Spartans progresses from the IVs and onward the question humanity will probably keep coming to is "how do we replicate the success of the Master Chief?" How is that done? Right now the UNSC's belief seems to be to make more armour, improve augmentations, have them train more and make more of them and do it cheaper. They're taking a very typical approach to the matter. An angle I might be interested to see at some point in the future is what if they thought they had succeeded one day? What if they made Spartans that, on paper, were just as good as and if not better than John? Better armour, better augs, better trained, cheaper, in bulk and even have Smart A.I companions that are 100% compatible with their carriers rather than John and Cortana's (what was it? 98%?). I mean it too, maybe they would even try starting some as children again. Throw genetic engineering in the mix too so that they can create candidates that would have met the SII criteria back in the day. Clone John even. Every obvious part of the equation that was used to create the Master Chief would be in play. That's what the UNSC treats the Spartans as, an equation they want to master, improve upon and perfect so that they can create the ideal product. And then I'd like to see the equation fail. Sure, they'd get some soldiers who's accomplishments end up going up there with the likes of Blue team and others of the sort but they can never recreate that thing about John that makes him special, the thing that's only ever been able to be described as luck. I think they should one day be able to succeed in mass producing super soldiers of the highest caliber but run into a problem where they can't recreate John's magic. Just from that premise for the Spartan projects future alone there's a lot of directions you could go. Personally I'd like it if it all went back to the human factor. The problem being that everyone begins focusing on throwing all these improvements on top of baseline humanity without improving baseline humanity in the first place. That's pretty much the what Halo's humanity is already anyway when it comes other facets of modern human civilization. If they want more heroes like John humanity needs to become a civilization and culture that acts as fertile soil for people like John to grow up in. In a way that's one of the ways I like to look at John's luck. Despite the fact that he was born into a future society that in a lot of ways hasn't developed much beyond our own modern one he was lucky enough to a live a life that forged him into the man we know him to be. I've just realized my entire train of thought might be neglecting the Librarian's meddling a bit too much but screw it. I like this better.
"Oh! I didn't realize. He's your pal is he? Your Chum? Do you have any idea what that bastard almost made you do?"