Being able to draw a planetary surface does not take into account MP - you need to provide instancing - that is why you do not see seamless transitions in ED, not because it is not technically possible graphically.
Yes agree - I've always struggled conceptually with some of the aspects of this and why it operates the way it does.
Especially with the transition between supercruise and normal flight (and vice versa) and I think there's multiple aspects at play here - 1. being the positional translation that occurs between your approach in supercruise and you "appearing" at a point outside the spacestation, asteroid field or other point of interest, 2. the setup/spawning of station/asteroid or whatever NPC/AI assets are needed in the location (which may already be there) and 3. the setup of the multiplayer "instance" of the players in the vicinity. One (or maybe a combination) of those factors is currently preventing a seamless transition between SC and normal.
Networking setup is probably the culprit here as positional translation is likely a "gameplay" compromise to speed up your arrival and avoid the pilot needing the ability to fly at SC speeds to within say 20KM of a station i.e. visible range before dropping out. Similarly spawning of assets is something that can be done on the fly based on proximity, so shouldn't need a transition, but might do if a lot of AI setup etc is needed.
Having a planet surface nearby wouldn't be any different to dropping into a planetary ring and I expect having a city/outpost there would be like dropping into a RES - I guess we'd need a dev to say which of the 3 factors above are limiting seamless transitions or whether it is sensible within Cobra's constraints to expect that the transition effects can be eliminated (or lessened) in the future.