>>> assumes that an industry has been identified already.
This is one of the key take aways from customer discovery - is your customer actively looking for a solution to the pain / problem you've identified. If your customer is actively looking for a solution than it is easy(ier) to identify and talk with them. If no one is looking for a solution then it may be that you haven't identified a real pain, you haven't identified the correct customer, or you are to early.
It's easy to say that you can't talk to customers because the industry hasn't been identified, but that is a bad statement and should be avoided.
Ideally you'd be a user of your own product, someone who is actively experiencing the pain and is looking for a solution. Then you'd look for people like yourself.
Otherwise you still want to follow the general pattern of talk to whomever stands to gain the most from your service. Note that the person that stands to gain the most might not be who you first assume it is.
This is one of the key take aways from customer discovery - is your customer actively looking for a solution to the pain / problem you've identified. If your customer is actively looking for a solution than it is easy(ier) to identify and talk with them. If no one is looking for a solution then it may be that you haven't identified a real pain, you haven't identified the correct customer, or you are to early.
It's easy to say that you can't talk to customers because the industry hasn't been identified, but that is a bad statement and should be avoided.