How long do you think it would take to write a simple data-oriented 3D - Game Engine with c++ and Vulkan?
Simple in a sense of graphically low performing. And all that alone?

Never did that, but being interested in game dev i'll try to help here.

Depends on what you consider for it to be done. You could code some simple game loop in a day i guess, and anything graphics related i guess is simply dependent on how much you want it to handle. Depending on your skills and free time and motivation i guess anything between week and month.

But that's just a guess

Nice idea.

good luck. but expect alot of PITA moments...