For reasons, the predecessor cluster is running a 'stable' platform, and hasn't been tracking the most recent updates. 

It's a snapmirrored cluster. 

I'm trying to figure out migration routes now. 

Is there any equivalent of 7-mode -> CDOT TDP replication, or am I going to have to bite the bullet and do an update on the source cluster to a newer version? 

And if so, because the snapmirror relationship that already exists, does that mean a 'stepped' approach of 8.3->9.1->9.4 (to 9.5 potentially) because that's what I'll need to do to preserve the snapmirror relationship with the replication partner? 

I'm not overly keen on pushing up a major version number on both our prod/DR environment  but if the choice is that or 'rsync/xcp' then I'll probably go with that.

I am just hoping there's a migration-assist option that means I don't have to do that, analogous to TDP from 7 mode.