As a hosting provider a change that would provide more clarity to my clients placing upgrade/downgrade orders, would be the inclusion of the regular recurring amount of the new product.
Currently the order confirmation email order_details merge field exclusively displays the details of the upgrade order with the prorated price paid or credited. In my opinion it is valuable for clients to have an email record of the regular recurring amount of their new product as well.
All our clients call or email us and we place upgrade/downgrade orders via the admin area for them, so they don't see the full summary on the client area purchase flow. The email sent out is lacking, and each client asks us what is going on after they receive it.