If you can engineer for two dimensions, you can engineer for three dimensions. A large part of my career was devoted to studying book-on-demand printing. I designed systems, wrote lots of code, printed thousands of books of all shapes and sizes, and traveled a lot.
At the same time, I've come up with hundreds of other products, some one of a kind (like a cute engraved toolbox for my son), some mass-produced. In high school, I started a company called Gamma Enterprises with some friends and our first product was an LED flasher pin, where the LEDs were bunny eyes. We printed 10,000 of my bunnies on plastic discs — and never went into production.
I've also experimented with the question of repairing lots of electronic gadgets. This often painful exercise teaches me a lot about engineering design and technological ethics. Still other things are only concepts, in dozens of notebooks, and in drawings in my flat file. Ceramic designs. Electronic circuits. Plastic gizmos. Some things viable, many not. Years and years of this. I am plagued with good ideas. But you must murder your darlings.
There is also a lot of this genre under Systems.