Facebook's market position is certainly enviable but I (perhaps naively) think they will eventually be dethroned. WalMart was the retail king... until Amazon came along. I haven't heard a "WalMart kills small businesses" rant in at least five years. They've been replaced. Facebook will eventually suffer the same fate.
But there is very little left to innovate. Almost all kinds of apps are there. AGI is only possible by large corps because of the massive compute requirement.
The next Google/Facebook will be made when either of the following criteria are met:
1. They mess up hard, causing a critical mass to boycott it (highly unlikely)
2. New world changing communication technology is invented, similar to the internet. With similar applications AND government regulations delaying them from developing on the new technology
3. Processing chips become so fast that the average person is able to afford and run a 1 petaflop computer just like the cost of buying and running a PC's today.
Amazon was possible because of the internet. Facebook will remain the King until some communication related world changing technology arrives.
