I disagree with this. Every "app idea" I've heard could be built, so going to a software developer and asking them whether it's possible is the wrong question.

I disagree with this. Every "app idea" I've heard could be built, so going to a software developer and asking them whether it's possible is the wrong question. Someone with an app idea needs to be asking whether there is a market for their idea. Figuring out whether an idea like OP's can be built is a difficult question for someone who doesn't know how to search for materials. In contrast, it's pretty easy for a mechanical engineer. OP is asking the right question.