Will this slow down at some point?
IME, yes and no.
As the material becomes less "fact-collecting" and more about integrating new ways of thinking about material, it slows dramatically from the pace that is obvious during those years from K through 8 material... on the other hand, if you don't have a kid who is a major bookworm, this kind of intensity can be a really rough ride.
I found it too scary to look more than a few months ahead when my DD was seven, honestly. I could barely keep up with her in terms of library holds and checkouts, much less trying to keep her in curriculum.
You should also know that this is about the time that we became increasingly concerned about credentialling-- because we were observing the same phenomenon-- it was dizzying, the rate at which she seemed to go through things. It was a bit like a step-function with random intervals. I couldn't predict how long something would work for her-- only that it was going to be way less than half the time that anyone would believe it took her.
Without credentialling, and some push on her weaknesses, we truly feared that we'd have a 10yo on our hands who would have more-or-less age-appropriate written skills (her particular weakness) and college-ready everything else. Oh, and because of the lack of written output, little way to PROVE it to anyone.
NOT what we wanted to have happen. So while I say that looking too far ahead was bad, on the other hand, you do sort of have to think about what happens when he does outstrip your ability to keep him "fed."
If his reading skills are not super-advanced, then he's going to hit a natural wall fairly soon-- the rate of absorption seems to slow dramatically at 5th grade + if they aren't getting it through ferocious reading rates. Auditory input (via being read to, or audio books) is just so slow by comparison. KWIM?
But beyond that, if he's a child who doesn't have naturally strong literacy skills, this is also going to be a major hurdle when he needs more than you can provide. You'll need to start lining up tutors, probably.
