I would agree re the potential for roaming to become a new billing moment for the carriers.
The EU forced the carriers to introduce EU wide non-roaming tariffs IIRC. Now we are out I would expect that they will all have a distanced dinner one evening and then they will all introduce a new "option" one month.
You will have EU wide tariffs and UK only tariffs to which you can add bolt on benefits that cover you for your holidays.
Just a guess.
It does mean that they do not have to do any home work as they just copy and paste the old documents they had 10 years ago!
