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Building the app is the easy (or at least the relatively easier) part of the bigger picture. The challenge is in finding the first solution to a business problem that's costing companies millions (or billions). Since you have the experience and skills to build a software product, I recommend seeking a dev/architect position in an early stage company that has (or is close to having) stage 1 funding. The rewards (both professional and monetary) can be significant. I strongly recommend not trying to find solutions to business problems - you won't have time to do any development if you're busy doing that.
Any existing app - that is written / designed poorly - is a candidate. Take a look at any of the available productivity apps in the app store and see which one is horse crap, and is a kind of project you'd enjoy working on.
I'd like to see an app that can make sound visible. It might not be a mobile app though.
Think along the lines of night vision goggles making infrared visible, but using sound waves and their frequencies instead.
Does anything like that already exist?