His goal is to somehow run a tunnel boring machine on Mars, right? He'll certainly be testing out new tech if that's the goal. These machines are magnificently heavy at present, aren't they?
He’s trying to parlay his life’s work into civilization on Mars. Everything he’s investing time and energy into has uses here, today, but the prize he has his eye on is not here.
Does making a tunnel boring machine lighter or smaller have advantages? Sure, if the machines get used to dig more than one tunnel then a more portable design will begin to develop. But nobody is worried about paying well over $1000/lbs to move the damn thing. And nobody is worried about how big a parachute you need to land it in Martian atmosphere without breaking it.
Knowing Musk, he isn’t spending time on this plan if it does nothing for his dream. Therefore there’s a connection. What might that be? What would digging large holes have to do with sending people to an environment with barely any atmosphere and massive sandstorms? Oh.
I expect solving that problem will take ages. If he starts now he might have some major progress by the time he’s gotten a few missions to Mars. By the time habitat management is a problem he may have something that is pretty crazy but not insane.
I also expect that when spending another $1000/lbs on cutting surfaces represents a net savings, you’ll see him working with some pretty bizarre and exotic materials. What that would be will come as a surprise to me, since I haven’t paid any attention to materials science since about the time they started making synthetic diamond.