Have you considered lasercutting or CNC milling as well? And what about lithophanes?

3D printers are highly accessible to people, even people with no technical knowledge can just buy one, download models and have it print successfully. Selling 3D printed parts pretty much only works if you do design as well and not many people request something like that. I don’t think you can make a feasible business out of 3D printing alone.

And there is mechanical design and aesthetic design, which both are completely different practices. I mean things like making a TV mount or a tube holder vs making a detailed Warhammer 40K model. You need different software and skills for both of them and it consumes a lot of time to do well.

CNC milling and lasercutting is not as wide spread as 3D printing is so you could still end up finding people interested in objects made this way.