I can imagine them pulling it off, if it's done in stages and not in a single expansion. "Landing on planets" doesn't have to mean "Walking around on planets" right away. It could go something like this:
DLC expansion #1: Walking around on your ship, and in station hangers, and whatever else they can squeeze in, like hanging out in bars to get BB assignments as an option to the in-ship method.
DLC expansion #2: Transition from orbit to atmospheric flight, flying over the planet surface and landing at a surface station. Walking around in the planet-side stations but not outdoors (i.e the identical thing they've already developed for orbital stations). Discovery of basic alien life, artifacts etc. by flying over and scanning the surface with your ship, but no actual walking around except inside surface stations.
DLC expansion #3: Walking around on the surface of planets on foot, elaborating on the game mechanics developed in the first two expansions.
Spread that out over 2 years development time, and doesn't look like that massive a project. Remember that the scale of the project will be limited by the gravity parameters. You'll only be walking around on planets and moons where the gravity isn't too far from Earth-normal. But getting back to the current topic, this only works if FD learns how to communicate what they're actually selling to their customers, and not yanking features at the last minute after taking pre-orders and paid Beta access.
