While setting it up I came across something called VirtualHere (https://www.virtualhere.com/) in the available apps install on the NAS (its basically a linux server) that claimed to let you use USB devices over a network to a USB server running on a NAS and thought whatever - sounds interesting. Then a few minutes later it hit me - I wonder if this works with dongles...
Yes - the damn thing actually works with iLok2 and that horrible Steinberg USB dongle and seems fine in Live for accessing plugins and Melodyne is happy with it, so finally my MBP can shed its chains (well being wired to a USB hub for dongles) and the dongles can now be permanently connected a USB hub connected to a USB port on the back of the NAS and can be trivially 'virtually' swapped between my PC and my Mac. (Obviously you can only use each dongle from one client at a time).
As for the NAS itself - I got the QNAP TS251+ with 2 x 4TB WD-RED drives (as a 4TB Raid 1 volume) and a netgear 8 x 1Gb smart switch (GS108Tv2) so I could team the pair of 1GB ethernet ports on the NAS giving it effectively 2Gb bandwidth to my network allowing it to serve my Mac and PC simultaneously at full 1GB ethernet bandwidth which it seems to manage just fine.
A handy service on it is something called QSync - its a simple file sync service that makes sharing Live projects between my PC and Mac transparent by syncing them in the background from Mac <-> NAS <-> PC. Another app for iOS called QFile lets me easily get at files on the NAS (including the sync'd project files) over the internet from my iPhone which is very handy for getting at .mp3 bounces etc, so overall despite being bought just as a decent NAS for backups etc, its actually turning out to be big helper for general production workflow etc and its really nice to not have to chose between nest of wires and fragile dongles connected to my MBP and dongle protected plugins use.