I can’t remember the Stripe jargon, but the whole plugin revolves round their old way of doing things (which allows credit card only) rather than the new way (which allows a wide variety of payment options).
Cancellation is described in a confusing way (from memory, it is cancellation of auto renewal but seems to be described as immediate cancellation).
I added quite a few topics about the plugin a while back. Many got no replies, so it’s good to hear you are working on the plugin now. Edit: here’s a link – Search results for 'tags:subscriptions @Jonathan5' - Discourse Meta