Perhaps this comment should lift you a bit more as well 😉
I have implemented quantity consideration for subscriptions. In order to test this, you need to:
1. Install testing version of the Stripe Payments plugin: https://s-plugins.com/testing-version/
2. Update Subscriptions addon to the latest version. Go to your WP Dashboard -> Updates, click “Check Again” button just in case and install Subscriptions addon version 1.3.3.
Let me know how it goes.