The 3D printer repair one seemed like a straightforward small business. However it is a very small or local market - hobbyists tend to know how to fix them on their own and big businesses get support plans from manufacturers. Not impossible though.

The bloom app could be either improved or even pivoted. Quite promising, but unless it becomes a real business or is really the best of is class it can easily be cloned and undercut.

The "smart" watch of this kind litters the Kickstarter for example... and it is too nerdy to scale.

Others are random hacks. :)