As to the rest of those assumptions, there is no reason to think that any of them are right: Productivity gains, for example, appear to be more of a measurement problem than anything else.
As to what tomorrow's business landscape will look like, just consider the recent past. Ten years ago, who foresaw a social networking site started in a college dorm becoming one of the world's 10 most valuable companies? And a decade ago who foresaw that what was once the world's biggest automaker would need a federal bailout to avoid going bust? What we do know is that some of today's leading companies will decline and even fail. Some will evolve, and maybe even prosper. Picking which is difficult, if not impossible.
Expand that question to the entire economy and financial markets. Will growth accelerate or fall? Will it be faster or slower than during the past 30 years? Will we enjoy a long bull market, or suffer the pain of a prolonged bear market? No one knows the answer; it's arrogant for anyone to say with any certainty that they do.
As I said before, the future is different from the past, and that means new winners and new losers. But it's important to keep in mind that long-term, economies tend to grow and markets tend to rise. That's something positive to think about.