The specific output (bhp/litre) and hence stress is pretty low for these engines (even with fancy cams) compared with modern motorcycle engines (often well over 100bhp/litre) or modern car engines.
With decent oil/regular drains plus well-controlled ignition/fuelling and no EGR, there should be limited potential for coking or other deposits.
My expection is that the limitations will be based on choice of materials in the valve train/piston rings/cylinder liners and there seems little evidence (so far) for problems in these areas
