Between bringing the ships back from Europe, training and implementing the new processes, and documenting everything for submission to the CDC, I'd be shocked if Disney could start that 60 day clock before February.
I wouldn't be surprised if Disney doesn't cancel everything before March in the next few days.
I agree... you want less turnover because with shorter cruises, the ships are exposing themselves to twice as many possible cases. HOWEVER, longer cruises also mean longer itineraries, and if you have an outbreak onboard, the cruise makes a beeline back to port with everyone quarantined. If the outbreak happens when the ship is at Castaway Cay, the ship is back at Port Canaveral within hours. If it's at Cancun or the east Caribbean, you are looking at a couple of days of people quarantined.