Hi, Del; you've probably already considered this, but a really wide sander is going to require a bit of HP to drive it. My chair-maker friend's commercial model is 5 HP!
I've noticed that most of the online DIY efforts have used plywood discs mounted on the shaft, sanded to a perfect drum, under power. A 4"+ hole saw would give you a lot of discs in fairly quick order (40 discs = 30")....hmmmm, maybe you're right; a turned roller would be quicker.... how about a conveyor roller? Or a turned hardwood one?