For one thing, this can't be done without a mouse to drag-and-drop with. This limits the extension of off-store extensions to those who can use a mouse, which is an accessibility issue. Are handicapped users or keyboard-only users just thrown to the wayside these days?
I was specifically asking about jonknee's use case, I never claimed that this would be an ideal solution for every other possible scenario. That said, your request to have a mouse-free way to install extensions is totally sensible, and I would be surprised and disappointed if they did not think of alternate ways to do that (perhaps using the command-line).
