Moved from https://github.com/backdrop/backdrop-issues/issues/1399#issuecomment-204...
As per @jenlampton's comment, this might be too hasty to implement in 1.x and should be better of for 2.x. Not setting the milestone right away. Waiting for more input.
...final step: move the admin pages for modules, themes and layouts as primary tabs of the same "Extend Backdrop" page:

Recent comments
In a blog post titled "Github Tips and Tricks for Contrib Maintainers", I'd like to see some of the following topics: When is the README sufficient for documentation? When should...
Github Tips and Tricks for Contrib Maintainers
Thanks Alejandro. That was the clues I needed.
Ubercart - Programmatically add product to cart and straight to Checkout
Have you tried uc_cart_add_item()? You need to provide the nid of the product. Then you can use backdrop_goto('cart/checkout'); to send the user to the checkout screen. uc_cart_add_item...
Ubercart - Programmatically add product to cart and straight to Checkout