I didn't realise that Hitachi had already built them all?
The Hitachi stock isn't directly replacing the HSTs. They are being replaced by a combination of timetable recast to release more 222s, as well as the introduction of 360s, and 180s
In which case I wonder if we might see HSTs continuing in service on the MML until the 810s are introduced.
I don't think HSTs will last til the 810s arrive. They'll probably live past the end of the year but as soon as the 360s start to get released they'll be going.