Richard MacManus put together a list of 10 future web trends and even though one of them is actually rich internet applications (with a quote from yours truly) but almost all of them have overtones of rich internet applications through them. Even the Semantic Web, which Richard lists first, is kind of intertwined with a better user experience. If we don't have to focus as much on the data then we can start talking more about the design which will be great for all kinds of software.
I think virtual worlds and mobile devices also have a huge role to play in the RIA landscape. Club Penguin was built entirely on Flash. And could World of Warcraft not be defined as an RIA? Mobile devices are going to be a huge part of rich internet applications because they expand the footprint. Tailoring a great experience to the mobile device is a fun challenge and the rewards are mind boggling when you think of the number of devices out there. Online video, another of Richard's 10, is also very closely tied to RIAs for obvious reasons.
The attention economy is the biggie for me. Richard describes the Attention Economy as "s a marketplace where consumers agree to receive services in exchange for their attention. Examples include personalized news, personalized search, alerts and recommendations to buy. The Attention Economy is about the consumer having choice - they get to choose where their attention is 'spent'." Google has made a truck-ton of money on the attention economy. But I think people are pretty sophisticated and that focusing on design and the user experience is going to be even more important as the Attention Economy matures. With so many people offering similar services, where do people turn their attention? They'll turn to the most usable, engaging, emotional, content-filled applications they can find. Richness will be a differentiator in the Attention Economy which is one reason RIAs are going to be such a big deal.