We are already tracked, they can already lock down your accounts, so unless you have TONS in your closet, you are already stuck.
Cash is expensive to make and deliver. It's obsolete and will be replaced by technology. Honestly the last jumping point might be 5G, it's faster and once it's everywhere it may happen. I believe the only reason it hasn't now is internet is not available everywhere. Once that technology hurdle is crossed, cash is gone.