You don't need to ask about adding features, just put in the ToS that the data will be used for app features and metrics for improving user experience.

Monetization by adding paid features falls well within those boundaries. Monetization by selling user data to whomever will buy it does not.

I'd really love to have a GDPR specifically for people like you who feel entitled to do whatever they want with collected data. I'd love to have had it when reddit decided to charge outrageous prices for the API.