First, work on three different mock-ups of your next-generation app, each of which is focusing on a different aspect of your initial ideas.

Establish a small-but-effective-enough tester group having similar aspects with your target user and conduct an emprical research through in-depth interviews in three stages:
1. Before they start using the new app
2. During their initial experience with the app and/or after some use
3. After they become an expert user of the app

It sounds a very traditional method, but it always works great if you are prepared well with your early mockups and questions during the in-depth interviews.

Second stage of the research is the analysis of the findings which brings you lots of original and innovative potential ideas waiting to be implemented on your next generation products :))

Please always remember to include your users in your development process to make it more custom-tailored to their needs.

Thanks!

veyis