Actually, the SEIO contrllers have been announced. I believe there is a thread in the equipment forum. The controller has been talked about for about a year, but is just now making it out.
I would say the main difference is quality. I have both SEIOs and Streams. Streams are the better product. But for the money, SEIOs are good too.
With SEIOs there are incidences of issues with restart after a power loss. It's a quick, simple fix - just nudge the impeller to get it going again.
With Streams, there really aren't any issues.
With Streams, you'll be happy having a top-rated product. With SEIOs, you'll be happy you saved some money. Overall, you'll probably be happy either way you go.
*Also, there are Vortech pumps that are coming out, but I don't know an exact date. The price will be closer to Streams than SEIOs though. You might look at these pumps though, just to cover all your bases.