I just don't think there is much demand for modified four strokes. You can buy a larger engine without any problem. If there were popular competition classes where displacement was limited and engine mods were allowed, there might be demand. I could see some demand the old time pattern event(I forget what it's called specifically) with displacement limits set to 15cc, but maybe the currently available engines are satisfactory, or mods are not allowed. I think there is more power hidden in most engines, but people are reluctant to take rotary tool to a 300USD engine. I've seen a few mods for increasing power in four strokes. I've done a few mods but nothing specifically to increase power at this point. I'm going to try a few in the spring.

If a car engine quits or breaks, the car stops. If an airplane engine quits in the air, the model's fate is very dependent on the pilots ability to land. Some can land any deadstick at their feet, some lock up and crash every time.