I was informed by one of my sources that Southeastern are still hoping to get a handful of 319s (their drivers are already trained for them) for them to use on the Orpington and Sevenoaks Metro routes, so that more of the 465s can be freed-up to to work the Dartford and Hayes services. That also frees-up more of the 376s for other services, and SE then probably won't inherit any 377s from TL or Southern.
This would essentially have had the same result as the 377s they were originally planning to get, so 465s that currently work the outer-suburbans would have been freed to do those all-important Dartford services.
One way or another, they get what they want.