Price inversely proportional to usage: stupid idea?

Specifically for an app (B2C) where higher usage doesn't incur significant higher costs.

To keep it simple, the idea would be to charge a fixed amount per month, and once a minimum usage threshold is reached, cancel the payment subscription and let the user continue using the app for free (forever, updates included).

Current thinking for why this is a good idea:

• Encourages customers to actually use the app.
  Aligns financial goals with customer goals (under the assumption that the more they use the app the better for them, ofc within reason).
• Reduces entry barrier and churn bc they know that eventually they will have it for free, and keep getting closer all the time.
• Makes explicit the fact that no customer stays around forever, but without the drawbacks of LTDs.

I am looking for counter arguments, or any observations really.

Thanks!