I watched nearly half of it and it sounds really interesting. This also gave me motivation to start program more myself and I will also try "Google Web Toolkit".
If it will replace email: Hard to say if it is really going to replace email. If it is going to replace it, it is going to take time for people to start using it and understanding that it is actually better than the old email system. Also, other companies will surely try to beat their attempt to take over the email system.
Googles "goal" if they have any might be the best in everything in the electronic topic. They first succeeded to make the best search engine over the Internet. Their search engine are "best" in many different ways. Most people are using it. They are using the best techniques for finding new websites and add the description to them etc. I'm sure most people would agree to that.
They have released satellite pictures from all over the world (Google Earth) and are the biggest and the only ones doing that too? Now they have started to make mobiles (android) and they have a good chance to be the best mobiles.
So actually, I think they will succeed replacing email with "Wave".