Still possible then but increasingly unlikely.
I'm fairly confident at least all the 745/0s will be in service by the time the 360s go off-lease so 321 substitution should be minimal by then. I anticipate the third Norwich service being pushed back until the entirety of the legacy fleet is gone, and then quite possibly eventually being abandoned, at least until the next franchise award. Most of the other franchise commitments were abandoned, so given the operational challenges of delivering that, seems fairly likely until better protection is put in place for franchise commitments or Mr. Corbyn has control of matters (context-only: I do not support that idea).