Routes are now effectively regions and the new regions are split into routes. All makes perfect sense.The LNE/Anglia Route boundary was at MP 98.40 near King's Dyke, a couple of miles east of Peterborough station.
Today's new NR Eastern Region includes several old and renamed Routes, and the East Coast Route and Anglia Route are two of those in the Peterborough area (East Midlands is another).
The local boundary between Anglia and East Coast Routes is probably still at King's Dyke.
From what one can tell, it's the Regions that now hold the power within NR, rather than the Routes.