Hi Adam,
I’m sure there will be threads and articles when it becomes clear how the Elizabeth line is going to work in respect of interchanges with two tube stations connected to one EL station.
It’s important to distinguish between OSIs with NR stations compared to LU stations. The Liverpool Street to Bank OSI is only with Liverpool Street NR and is intended for people using the Northern line at Bank and National Rail at Liverpool Street. The same can be said about the Embankment OSIs (District/Circle to National Rail) and the Marylebone (NR) to Baker Street for Circle, Ham & City and Jubilee lines.
The big difference with Moorgate is that there is only one station. National Rail comes in to the Underground station and indeed the NR and Northern lines are above one another. This is why I can’t see an OSI between Moorgate and Bank.