Since MML is coming to TSW3 with the EMT HST, it would make sense if they get added to SEHS as an AI only layer at St Pancras to make the station even more realistic.
SEHS has an extremely modern timetable- clas 43's rarely if not EVER go to pancras - it's 222s, 180s and 360s om the EMR platforms
DTG said that the SEHS Extended timetable is based on a 2019 Timetable and back then EMT was in the final year and HSTs were still operating so it should be possible.