I BELIEVE THE ADDITION OF THESE PROPULSION SYSTEMS WOULD TAKE THE GAME TO A WHOLE NEW LEVEL AND PERMIT THE CREATION OF CRAFTS BEYOND OUR IMAGINATION! It would also be SUPER awesome to mess with!!!!!

-more customizable and thrust vectoring jet engines
-ramjet
-scramjet
-hybrid rocket+jet engine (like the SABRE)
-marine propulsion options for boats and submarines
-rocket engines
-ion drives and thrusters
-electric propulsion
-antimatter propulsion
-antigravity propulsion
-variable cycle engines and supercruise capable engines
-nuclear propulsion
-laser propulsion
-microwave propulsion
-direct impulse propulsion (like particle accelerators)
-laser thermal rocket propulsion
-microwave thermal rocket propulsion
-plasma propulsion
-anti-matter drives and engines
-anti-gravity engines
-inflatable and deflatable balloons (refer to hybrid airship tech like lockheed martins)
-retractable helicopter rotors/propellers