That of course is a distinct possibility.Yeah, that's surprising on the face it but perhaps they're already working on it, have discovered it's really hard and are just looking for some bright young thing to really focus on the problem?
But also, looking at OP's quote from the job requirement again ....
As part of our gameplay programming team, you will work with Frontier’s proprietary COBRA engine and the game systems that create our simulation of the whole galaxy. You will build upon the physics, driving model, navigation and networking systems to create driving AI that understands and explores the surfaces of procedurally generated planets. Working in a cross-discipline game development team you will build an understanding of how vehicle AI fits into the wider game, and help the team to enhance the game with the opportunities that vehicle AI offers.
Let's assume for a moment, Legs becomes the Next Big Thing. They know there will be complaints about depth of gameplay, and this appears to point towards developing that. Which suggests development Beyond the Next Big Thing - the pre-development before "full development."
So, if we get new vehicles to drive around in on planet surfaces, or even bikes to skim over the surface, the possibility of NPCs on the surface of a planet to challenge us, or work alongside us, is yet to come.
I'd say it's looking healthy for the game beyond Legs. Either that, or they really were developing "only" atmospheric planets and much of the player-hype has made them realize that planet-based activity including Legs (and accompanying vehicles) is more important to us than they originally envisaged !
But, yes, I am speculating.