Start by calling SEO resellers. Ask them if they experience any challenges sharing reports with their clients. If they do, dig into what the problems are. Does your solution meet what they need? If so, tell them you are creating a solution they'd like and ask them if they want to buy it. Then you have two options: collect payment then and there for your uncreated product or add them to your list to contact when you launch. But first you need to validate that enough SEO resellers need the product you want to create. Start there.