Hi. thanks for this awesome game, i'm enjoying it alot :D
My suggestion comes in 2 parts, which would be unbalanced each stand alone.
1) Gravity generator <-> Artificial mass.
If an gravity generator affects a grid with artificial mass, the same force should be applied to the grid with the generator. Realismn! Gravity Drive Broken! Gravity Gun Recoil! woho! So you need to build an actual "Mass portal" if you want to move your ship with gravity, and is has to be heavy and well thrusterd for dampening.
2) Max speed depending on source.
Something like Athmospheric 90-110 depending on Atmosphere density. Ion 100, Hydrogen 150, and Gravity 250. Realismn! Actually really dangerous player made weapons! Making gravity portals rewarding. Would make grav drives overpowered without 1).
3) oh and could you pretty please add missing slope corner blocks? atleast the 4 blocks needed for low angle 2*2*1 courners?