I thought I heard or read somewhere that someone had actually gotten EPOC r5 to run on the PocketPC platform. The iPaq runs on the same StrongArm processor so I am sure it is possible. I was a Psion user for the better part of eight years and was the proud owner of a 3a, 5 and 5mx. I have given up all of them except my Series 5 (just in case) for a Compaq iPaq. The PocketPC doesn't hold a candle to the Psion, but I really couldn't take the screen anymore.
My main problem with Psion has always been there lack of interest in advancing their technology. Yes, they are functionally better than the PocketPC's, but they made no effort to engage the competition and come out with a color handheld. They also lacked in trying to break into the American market.