I don't think there should be a hiatus from the rules, it undermines EVERYTHING we've been told / instructed to do. Nobody would need to spend Christmas alone because of single household bubbles.
Yes, people would have broken the rules - as they are already doing. But people are going to break the Christmas rules, too. They'll either find their "but it's ok because..." or they don't give a toss anyway, and won't stick to the three households rule. Or they'll meet people either side of the five days allowed. Or they'll gather in pubs etc.
We're in lockdown. We're going to come out and there will still be tight restrictions destroying businesses and people's livelihoods. We've been told these restrictions will last until at least April. So if all that is required, WHY are we risking another rise in infections in January - when the NHS normally struggles at the best of times? We either need to be in lockdown / tiers, or we don't.