Actually it's also limited by tons of factors: competition, fashion, etc. People have been announcing the "end" of the iPhone and iPhone killers ever since 2008 (that was BS of course, but it still can happen that some revision, e.g. 6s sells less than the previous).

iPad for example has had that happening to it (later revision sold less well).

iPad is much more niche compared to iPhone. Not everyone wants/needs a consumer device to lounge around with for the price point. Everyone wants a phone. And to people like me, the iPad keyboard is simply unusable in landscape mode. Has this changed? No idea why they insist(ed) on stretching the keyboard across the entire screen instead of leaving half of the keyboard accessible to either side with thumbs. Even if the keyboard has been updated, the larger form factors are just too large and clunky for 2-handed use.

You can tear apart the keyboard in two halves you can use with either thumb. Admittedly a well hidden feature.

Hrm, I'll have to try one out with that setting. I have both a MacBook Pro and an iPhone, but being able to watch video on a tablet while lounging around would admittedly be nice. I suspect the device will still be too bulky and heavy to comfortably type on for longer than a minute at a time, even if the keyboard allows for it. I'm always puzzled when I see a photo of someone typing with 2 hands on a tablet while lying down. I can't imagine physically arranging myself in such a way that this is even possible.

Well, at some point it's limited by population...

Not really unless we hit zero population growth world-wide. Otherwise, there will always be more people to buy.

We are likely to hit zero global population grown sometime between 2040 and 2070. It's not around the corner but I hoping to still be alive at that point. https://en.wikipedia.org/wiki/Projections_of_population_grow...