OK, so the question is "what will be the next giant wave"? What about "will people use whatever the next giant wave will be instead of Facebook?" IOW, will the next big think overlap enough with Facebook usefullness to mean a hit for Facebook?

Supposing the answer is "yes", I'd say FB flaws matter a lot. Even flaws that users don't see now as such, maybe because they see them as unavoidable. What if a new service, based on another model, arised and it hadn't such flaws?

No, the next giant wave will not overlap with Facebook's wave. Whatever overlaps with their wave, Facebook will be on top of. People will use whatever that next big thing is along with Facebook, not instead of it.

But you're assuming that there isn't anything that people will choose to use instead of Facebook. I think it's possible that Facebook could be supplanted by another platform.

There'll always be overlap when a competing platform comes into the picture - so any 'death' will necessarily be drawn out.

I like your wave analogy, because it highlights the way that these service-orientated companies are tied to the current socio-economic landscape. This helps to show how competition between companies isn't the most important factor. A change in market conditions can prove just as disastrous (as a good competitor) for a company like Facebook, and this kind of change is probably more likely to signal its demise, because a market-leader's success tends to increase exponentially when conditions stay the same.

I think the most interesting question is; what change would be necessary for people to migrate from Facebook to another platform?

It will happen - but when and how?