Well right now anyone can enter a jet into pattern and weight would not be an issue. Look at the Kolibri turbine. It is smaller than a soda can. The only rule that might prevent one from using it in pattern would be the noise. Also AMA rules do not restrict the use of jet propulsion. I'd love to have someone enter a jet in a contest. I bet it will be really hard to perform a stall turn and make the noise limit. Unless it has thrust vectoring... I recently heard a prominent jet manufacturer talking about the possibility of jet pattern... But that is a totally different topic.