In the current publication of Rail (774) it says that Network Rail has moved its target date for ERTMS "50 years hence".
ERTMS requires In-Cab signalling, computer control, and a digital gateway into the train. Obviously this would be way beyond the finances of most classic locomotive owners....so ERTMS would effectively kill mainline steam.
The original roll out for this on the southern part of the ECML was to be 2021. That's going to come around pretty soon.
But now NR has effectively thrown away its "Digital Railway" plan.
So maybe it'll be 2071....or even later.
Don't rush into it NR, we don't mind waiting
BW