Seems like a lot of people work for a long time perfecting their special flavor of ice cream and never quite get to the cherry on top.

A lot to be learned from building a 3D engine, no doubt, but anecdotally the chances that it will lead a working game that anyone wants to play seem low. That's not a bad thing, unless they tell themselves they are going to ship a game any day now, just as soon as they do X, then Y, then Z, ...