Privacy is as much a feature as it is a business model (or reaction against ad-based business models). The biggest question to consider is what will you replace

Privacy is as much a feature as it is a business model (or reaction against ad-based business models). The biggest question to consider is what will you replace that business model with? And will people pay to use software they're used to getting for free? I'm not super confident the answer to #2 is yes. But that's the kind of market research you should do before jumping in. The other alternative is to follow in the path of Signal, make a free, open-source alternative. Survive on grants and donations if you're lucky.