I would like to suggest that he reveals the app to a small group in order to get feedback on how people like the app. He said that he released a similar online version and it got good results. I still think he should attempt to get feedback before he creates the app. Am I asking him to take an unnecessary step before launching
Absolutely not. I do some part-time work for Growthhackers.com run by Sean Ellis and anyone on that site will tell you testing is crucial.
I don't know what vertical the app operates in, but not getting feedback is normally someone's laziness or fear of rejection. Predicting consumer behaviour is exceptionally difficult so why not let them provide you with clues.
Clearly any entrepreneur needs to have a vision and a set of core values - but then it's best to perform high tempo testing and collect meaningful data.
Online and mobile aren't the same experience - one is asking a user to sit at his desktop, the other is asking him to install it on his phone.
I mean how difficult is it to get user feedback even using a mockup tool like Axure, Mockingbird, Balsamiq etc.
I guess I would want to know what the levels of engagement were from the online test, have those users been retained and communicated with to become early adopters for the app?
To be honest if the dialogue between he and the online users has died down, then it shows he has no commercial acumen. They are prime candidates for feedback on how the app should work.