I have been reading reports that as PTC systems are being certified for operation, their data transmission facilities are being used to transmit various mandatory directives such as Track Warrants, Temporary Speed Restrictions and Work Limits. Moreover, company issued electronic devices are also being used to send the same type of "paperwork" in various electronic formats. Previously read over open channel VHF radio to be copied and repeated by the crews, the new methods keeps the information off the air with the radio link only being used to confirm delivery.
Although a loss for the scanner community, delivery of what I will call "train orders" has used closed communications channels since the first telegraph line was established to replace a pure timetable system. Hand and telephone delivery have always represented a small, but durable portion of train order transmission since radio communications became a thing in the 1970's. Closed communications channels have long been the norm in Europe using a dedicated GSM-R band set up for the purpose.
I would still anticipate policies on train order transmission to evolve as one of the greatest benefits of open channel communications is the situational awareness provided to all manner of right of way workers and train crews who may wind up at the wrong place at the wrong time. There are countless stories of accidents averted because someone was tipped off to an unsafe situation through radio chatter and is also one of the reasons signal calling remains a thing.
It will be also interesting to see how the scanner community adapts and if PTC deciding will become a thing like ATCS decoding. Although not as open as analogue VHF, there are no FRA requirements to encrypt PTC data, only requirements to authenticate safety critical data. What the industry has decided to do remains to be determined, but with locomotives needing to be able to operate across the national network it is highly likely that industry will seek to minimize the certificate management problems. It is also likely they will just do a bad job resulting in security that is easily exploitable.