updating card directly from product view.

Hello,

I know this isn't at all what you ask for, but do you know that you can directly update product quantity in your Cart, see my screenshot :

I suggest you this because, it's quite close and can be set up very quickly, while to have exactly what you requested this will need lot of custom development.
And if you want go for it, we can propose you a quote but before this will need more elements to better understand your needs through a concrete case, and be sure that your needs can be complete via some settings (even advanced setting).

Awaiting your returns to progress on your subject.
Regards