[Robotbeat]

Sure, but then your economy is still constrained to grow at the speed of light. A shell of some thickness expanding at the speed of light. The volume of that shell increases parabolically, not exponentially.

So it still needs to slow down growth, although growth can still occur indefinitely. Well, billions of years until stars naturally start burning out, in which case you get a slowing of growth and degrowth until you're huddled around red dwarfs for a trillion or so years and then harvesting energy from black holes until like a quadrillion years.