A Turing complete scripting layer run by the full clients (mining nodes) is subject to the Halting problem. You are begging for Murphy's Law due to centralizing chaos.

When we run JavaScript in our Chrome browser, we are not requiring Google's servers to run the scripts. I see your mitigation is to charge the contract per line of code executed (beyond 16) for each transaction on the contract. However the cost of execution is "not one size fits all", thus you prevent innovation and bind together that which should be decentralized freedom.