The product they are building is for the healthcare system with the major target on healthcare workers. They are focused on communication, collaboration and scheduling.
There are a few things to consider:
- Will the lack of market value reduce the viability of the company and hence reduce your job security?
- Does the lack of market value reduce your passion and enthusiasm for the work?
- Does the lack of market value imply some fundamental issues with how the company is run (in that they are trying to build something that likely won't sell)?
I would suggest raising these concerns with somebody at the company. If they can put your mind at rest, then you should feel confident to proceed with the role.
Your realization is out of scope...unless part of your scope is to refresh its business case. I suspect it's not, so what you realize or don't realize is irrelevant. And if you spent time doing the market research you would need to do to determine a product's viability in the marketplace, I would not bill your customer for that time and effort. Again, because that work is out of scope.
Just build the product and deliver it.