The question of manpower is not a problem as refs have to retire at a young age so it would be easy to have a retired official who is unable to run and ref the game but is quite capable of watching a tv monitor with radio connection to the ref. It will come it is just a matter of how and when it will be implemented..
The retirement age for referees has been discarded as it fell foul of age discrimination laws.
You'd still need to teach them how to operate the video machinery, and old people are notorious awkward with modern technology (heck, some younger officials have trouble operating the subs board!)
Unless you're suggesting they watch tv and re-ref the game at the same time, still undermining the ref and going against the basic tenet of referees being the ultimate authority on a given match.