@ Nicholas, I cant imagine there are very many cases where you need to replace the heatsink itself (short of damaging it while you have it removed from the case). But being an Android device, I can imagine someone will find a way to overclock this little box to squeeze a bit more performance out of it and make those forthcoming games run a bit smoother.
In that situation, you most certainly would want to replace the heatsink with something that provides more surface area for cooling, or perhaps even active cooling. But you may also find users removing the stock heatsink, lapping the base, and reinstalling with a better thermal transfer material in an effort to improve cooling.
But you are right, without a fan on there by default you probably will never need to "service" the heatsink. It would be difficult to make something this small, and this affordable by having a slot and socket for everything, but making devices more repairable is always a good thing.