Just got a round of changes for March last night - second round of changes on a/c types SFO-EWR in the last few weeks and some east coast EWR flights with times moving around.
Second time in 30 days that the same reservation has been rebooked out of O to flights without O, and unsurprisingly downgraded. In each case I've been able to rebook back to O at the original (as far as I can tell, "saver") price of 30k points, but am expecting battles as schedule changes roll through closer to the trip time and seats start filling-up.
I'm a fan of PremPlus but it's just not reliable to book on transcons.