I had to disagree, because the propulsion from solar sails is extremely slow. Extremely. Did I mention extremely slow? It's a concept based on getting stuff out of the inner system over the course of years. That is not a fun concept for a space game. A space simulator? Maybe, but I don't think StarMade is designed as a space simulator as much as it is a space game.
With that, I need to contribute a replacement idea. I'll pull from real, actual propulsion ideas, like what you will find on space.com.
1. Mini-explosives dropped like mines and immediately set off directly behind the ship to "kick" it forward. This really isn't much different from Starmade thrusters if the sequential explosions are close enough together.
2. Light-pulse propulsion, which is very similar to solar sails, but uses a laser (or maybe a particle beam), and bounces off a 45 degree structure element, to bounce the beam out to opposite sides of the ship, while the combined forces produce thrust.
3. Short-range teleportation as a simulation of short, temporary worm holes.
4. The new space-warp propulsion theory where the space around a ship is warped in such a way that there is a gravity/space wave "pushing" the ship forward, while a space-warp in front "pulls" the ship, essentially causing the ship to "fall" forward. This is also not much different from Starmade thrusters. It could be a great way to add a small number of blocks to ships to greatly increase speed without increasing turning rate.
5. Not so much a thruster mechanic as a slow-down mechanic: Airbrakes touching a planet's atmosphere a la the movie "2010 (The Year We Make Contact)".
6. SCRAM jets. Starmade Thrusters with a thrust bonus in atmosphere.