Again, how exactly do you propose that "get a message when CTRL-V is clicked" would work with:
- raw keyboard modes (in which an application gets input straight off the keyboard because it wants to do its own keyboard processing)
- graphical context menus (user clicks on a paste button within the app, or even uses a voice or other control - how does the application communicate to the OS "my user wants to paste"? Or does your back-of-the-napkin fix require users to only use devices with keyboards and only use the keyboard?)
Amongst other technical considerations. It's almost as if pretty much every major OS/windowing system has ways of programmatically accessing the shared clipboard for a reason.
Currently: application queries clipboard state and gets back some structured data. (quick googling confirmed this).
Proposed: application gets a message when CTRL-V is clicked along with the same data that currently gets returned when clipboard is queried.