seamless planetary flight should only be done if :
A. gravity is simulated - and idiots who chose thrusters too weak to escape the gravity of a world without a means up purchasing a bigger thruster should be stuck there or if available, purchase a sidey and abandon their ship at the planet-side station. Hint: Escape velocity of earth is 11.2km/s and the fastest ships currently in the game boost at around 0.4km/s
B. If you enter a planet with a cracked canopy, if the planet is not earth-like, the likely poisonous and/or corrosive atmo will kill the pilot.
Seems more realistic to implement space elevators and atmospheric specific ships. This would have the side-effect of only being able to enter/exit planets with elevators.