100km is nice for sightseeing purposes and deep immersion.
But lets take a look at how long it takes the current ships, at current max speeds, to travel 100km:
Sidewinder: ~7.6 minutes
Eagle: ~6.8 minutes
Hauler: ~8.2 minutes
Adder: ~7.6 minutes
Viper: ~5.3 minutes
Cobra: ~5.9 minutes
DBS: ~5.9 minutes
T-6: ~7.5 minutes
DBE: ~6.9 minutes
Courier: ~5.9 minutes
Vulture: ~7.7 minutes
Asp: ~6.5 minutes
T-7: ~9.1 minutes
Dropship: ~9.1 minutes
Clipper: -5,5 minutes
Orca: -5,5 minutes
FDL: ~6.2 minutes
Python: ~7 minutes
T-9: ~12.8 minutes
Anaconda: ~9.1 minutes
Assuming those times can be shortened by ~20% by use of boosting, it is still a long time to stare at the screen every single time one lands on a planet. This on top of the time one already has passed staring at the screen while approaching in supercruise.
At first people will be staring at the landscape, and all the new detailed planetary surfaces. But after a few dozen times...
I would give it 3 days at most before mass complains begin to shower FD's office.
Unless there is a new flight mode with higher speeds for planetary flight, or space to planet transition, the drop would have to be closer than 100km.
Anyway, however FD decides to take on this, I will be looking forward to it!