I would be leery of anything 3D printed for this application.

I am not sure what your overall goal is with the "handlebar extension" and how you intend to use it with "bags", however...

When I was researching bikes one of my riding partners mentioned having the steer tube of the fork cut "high" instead of sized up and cut to size. A tall steer tube can be tamed with spacers, its kind of hard to go the other way.

With a tall steer tube you can add a 2nd stem. On that 2nd stem you can put a dummy bar for... bags and accessories.

This is what I did on my touring bike and I have enjoyed using it. The 1st dummy bar I put on was too short. It was sized to fit between the loops on my drop bars. I added a mirror to the left side and when I loaded up the bike the mirror was too far in to see past the gear on the back. So I extended it I want to say 6-10" more. I have just enough room to see in the mirror past my gear without being too obnoxiously wide. It does stick out there, but I'd rather have it set up that way than not have the visibility.

Food for thought.