Do you think anything similar to the "end of novelty" could happen within a human's current lifespan?

I don't think that could practically happen. Though I suppose people do often end up feeling that is the case in their own lives.

Also, is novelty necessary to have a life with positive value? Could you not imagine yourself living a routine for x number of years (where x is less than the current human lifespan, but greater than 10) and being happy?

I do think novelty is a key component in happiness. Not necessarily that you have new stuff in every moment or day, but at least that their is the potential for novelty.

If so, why do you think this would change for a sufficiently large value of x, and why don't you think that you'd be able to find a new routine?

Perhaps for any non-infinite value of x, you'd be okay. Once x could be infinite, I think there could be the realization that everything is pretty meaningless. And I don't see much reason why any non-infinite years as a lifespan is better than any other. I suppose reaching an age where you could have kids or grandkids might be a good benchmark. But the difference between 100 years and 200 seems arbitrary. As does the difference between 1000 and 1,000,000.

Also, what would be artificial about a "perpetual invention of novelties" - what makes perpetual novelty artificial that isn't also the case for current novelty?

It's a good question. I don't know. I can just imagine coming to the realization that (a) I could live forever if I choose, and (b) everything could be done given enough time, of which I have a limitless supply. If these are the circumstances, every challenge would only appear to be a challenge.