Hi Matt,
I'm fairly sure it can be done, although I haven't done it myself.
I have migrated a destination from one SVM to another which, given the separation between SVMs is complete in order to allow for multi-tenancy, it is almost the same thing.
The only real difference to 7-mode is that you need to set up all of the peer connections, so you will need to set up cluster peering between NY1 and NY2 and between LDN1 and NY2. You will then need to set up the SVM peering between the relevant SVMs.
The Snpamirror Initialize command includes an option to specify the source Snapshot whcih you will need to set up the mirror between LDN and NY2.
The biggest issue I had was removing the old Snapmirror base snapshots. For this I need to go into advanced mode so that I have the -ignore-options option for the Snapshot Delete command.
I can't remember all of the details as I only migrated a couple of volumes and it was months ago... hopefully the above helps.