How do most people navigate a boat? They plot a direct course to their destination and motor away. This works for short trips, but for longer journeys you will end up hundreds of miles off course. Why? Because wind, current, seas & pirates can have more influence than your motor. A boat operates in a system in which its own capabilities only influence its movement, not dictate it.
Forecasting into the future is a lot like navigating a boat. Probably 90% of the forecasts I read are written by people who believe that their product or idea is self contained and will dictate its own movement. Most of the predictions I have read about Open Source, SOA and SaaS are of this variety - they will likely be wrong.
I don't have the perfect software prediction to offer, but I know what it would look like. It would recognize the inertia of current ways of doing business. It would identify the possible impact of different environmental factors. Most importantly, it wouldn't treat itself as a self contained entity. Separately, you can talk about Open Source as a movement to produce non proprietary software, SOA as a way to extend capability and SaaS as a novel distribution method. Personally, I think that software's future won't be dictated by how these key trends act independently, but how they converge into some kind of megatrend to influence the landscape. Any company that isn't considering this convergence is likely to end up a long way from its intended destination.