Why not offer both? Paying $10/m for as long as you like and get all new and old courses. A basic streaming subscription essentially.

But for $100 get lifetime access to only that one purchased course?

Then if the consumer wants more they have the option to spend another $100 for a different course or add the $10/m subscription for other/new content.

I personally would benefit from this immensely in course style learning. I tend to browse lots of content until I find the right info. Then deeply consume the single topic slowly as I teach it to my team. I'm usually stuck paying monthly for something I use for a month then don't use until I begin the training a few months later then dormant again until the next training x months later.

An example.. pay for a Spotify/Netflix/etc monthly subscription but have the ability to purchase a cd/series/movie/book so that if you end your subscription you still have access to the purchased items. Essentially paying a monthly rate to peruse through material then purchasing to deeper dive/repeatedly use an item. The service might even make more money this way.