It will not just be MH systems that will need to be "turned on" for them to join. All members would have to do test/integration work as well and most companies in the Western world have change freezes during the December/January period, and we know it is a peak travel period so there is no way I would want to muck around with booking/reservation/frequent flyer etc systems in this period.
1 Febraury seems to be the agreed date even if all members were ready to go live with MH membership as the risk is too high.