On the other hand, no one has mentioned technology. Why expect such a big boon to stop at bitcoin's current development team and code? Why wouldn't something better than bitcoin come along by then, fueled by the then common knowledge the developing such a solution would be profitable for the producer and participants?
Take this same argument and think Internet instead of Bitcoin. Or, more specifically, IPv4. Why hasn't someone developed a better protocol than IPv4 and have it take over the Internet? There is tons of money in it, think of all the routers you could sell!
It hasn't happened because IPv4 is entrenched. Switching to something else is too much work. A new protocol would have to be better than IPv4, and not a little bit better, but MASSIVELY better to make it worth while. And, and BTW, there IS a newer, better protocol and its called IPv6. And it is being adopted, but very very slowly, because its a bunch of work and IPv4 is working and is "good enough".
And that is why Bitcoin is in it for the long haul, its got the head start. In business terms this is called the first mover advantage. Sure, Bitcoin is really small compared to the Internet/IPv4, but in terms of cryptocurrency it is way out in front. For it to be replaced there will either have to be a catastrophic failure of Bitcoin, or the replacement will have to be massively better.
Its also why Litecoin will never get much traction. You could argue that it is better than Bitcoin (I wouldn't), but even if it is, its only *slightly* better, and that will never overcome Bitcoins head start.
Note: the first mover doesn't always win. In some kinds of business being the first mover is actually a disadvantage. But in terms of technology like this first mover almost always "wins". Unless they had the right idea, but screwed up a fundamental aspect of the technology. I think its pretty clear that Bitcoin is solid technology.