Hi Andrew,
Because flying en route sectors has relatively fewer interactions with ATC, it would be possible for pilot initiated interactions to be supported by AI ATC when flying an unstaffed sector. The result would be an improved immersion for the pilot because, during the whole of en-route flight, ATC would be 'available' at all times.
Examples:
Simple, pilot "Request level [level]"; AI ATC "Climb to [level]/and maintain [altitude] "; pilot"Climbing to [level] "
More complex, on entering a sector with approach control on duty, AI ATC "At [position] contact [unit name] [frequency] "; pilot "Wilco"
Flying in an en-route sector where live ATC comes online, no action
Flying in an en-route sector where live ATC goes offline, no action
Only a small subset of CPDLC messages would need to be supported to give pilots a feeling of being in on-going contact. Transfers between live and AI ATC would be transparent. The implementation of CPDLC within, for example, PMDG Global Flight Operations would be complemented by the AI ATC within POSCON.
I hope this helps.
Any further details, please do ask.
Kind regards, Richard