The power of Archicad's work ergonomics resides in its simplicity and in the bridges that archicad creates between an object and its edition without going through menus and submenus. I think that adding a second button to reserve an object (while it is already being edited) is not going in the right direction.
Working in teamwork works like a communal library : if you want to modify or print a book, you have to BEFORE booking it. A great Library cause you can put books into this library without permission 😉
This is an already working BIMcloud only feature - the Reservation Assistant (or so called "autoreserve" does the same thing - if you forgot to reserve an element prior editing it, ARCHICAD automatically reserves it for you.
As I said, it is BIMcloud only, which means, it requires BIMcloud User Licenses to be able to use.