I have the same request, but I feel I can add a bit more clarity to the issue. The “All Products” plugin referenced above simply adds the front-end bit to add any product to any subscription. On the backend, the subscriptions plugin is mostly, if not completely, unmodified. Subscriptions are simply created with any products, rather than only “subscription” products.
Therefore, the actual implementation in this plugin shouldn’t need to interface with any features of the “All Products” plugin. All we need is a feature for checking and updating the pricing of any product(s) that are part of subscriptions, whether they are “subscription” products or not.
Is that something you can do for us?