You'd roll it out as it became convenient. Things need to be replaced.
This transition will take several decades, as those cables are not in need of much maintainance. But it could be done.
Who would pay for the change, though? I doubt the ISPs are going to do it, the current system works for them. The house owners won't, for the same reason.
Yes, it can be done. I wouldn't bet on it, though. Most likely, by the time this transition is over, all the cables are obsolete. That's one of the reasons nothing like this has happened so far - the players in the field are afraid that their investment will be outdated before it is amortizied.