The way that this works is "containerization" or "sandboxing", which can give an IP to anything ranging from one running binary to a large collection.  I started the current effort using Docker containerization, but its standard setups require a lot of filesystem recreation, each Docker container has an entire working OS filesystem apart from the kernel; but during the studies for Docker, I blundered into something else called firejail, and firejail appears to be just what the doctor ordered, it seems to do just about everything while using the existing filesystem, and one can very easily turn off the features one doesn't need. 

To cut to the chase, after boot and system prep, first one creates an IP bridge:

sudo brctl addbr br0
sudo ifconfig br0 10.99.99.1/24

and then starts JACK in the sandboxes:

# The master hardware sandbox is named MASTER, the QJackCTL profile is named MASTER,
# the JACK server is named MASTER.
nohup firejail --name=MASTER --noprofile --net=br0 --ip=10.99.99.10 \
    /usr/bin/jackd -n MASTER -m -dalsa -r48000 -p256 -n2 -Xseq -D -Chw:NVidia -Phw:NVidia \
    > ~/LOGS/jack-master.log &


# The SRO hardware sandbox is named SRO, the QJackCTL profile for it is named SRO,
# the JACK server is named SRO.
nohup firejail --name=SRO --noprofile --net=br0 --ip=10.99.99.15 \
    /usr/bin/jackd -n SRO -dnetone \
    > ~/LOGS/jack-sro.log &


# Ditto for STRINGS.
nohup firejail --name=STRINGS --noprofile --net=br0 --ip=10.99.99.20 \
    /usr/bin/jackd -n STRINGS -dnetone \
    > ~/LOGS/jack-strings.log &

And then connects the JACK servers, by adding jack_netsource processes into the existing MASTER sandbox:

#!/bin/bash

# SRO
nohup firejail --join=MASTER jack_netsource -s MASTER -H 10.99.99.15 > ~/LOGS/netsource-sro.log &

# STRINGS
nohup firejail --join=MASTER jack_netsource -s MASTER -H 10.99.99.20 > ~/LOGS/netsource-strings.log &

I have not tested further yet, no clients -- am working on something closer to production now -- but this is looking very good, the connections are reported successful, zero xruns, and on this prototyping box -- 2.6GHz AMD quad, ten-plus years old -- 0.8% DSP in use on all three JACK servers and very low memory usage.  This is considerably better than I had hoped.

The sandboxed binaries above, cannot reach outside the one box as written above, but the excellent and very responsive developer of Firejail has provided a method.  As a result this could all be done  box-independently -- for instance, if one's "monolith is the building" (going to have to remember that, Patrick), one could have all indicated motherboards NFS or SMB to one file server, and then use a central control GUI machine to run all firejails on whichever hardware was proven most appropriate, and testing could become much easier.  Along the way I also found 'xpra' likely to be a very good way to setup such a central control, am going to test that as a side project.

I tried using netjack2 first, but ran into mystery behavior, xruns started piling huge when the second slave connected.  So I went with netjack1, especially because Patrick Shirkey already proved the above paradigm in multibox mode using netjack1.  I am currently using netjack1 under jackd2, but will change to netjack under jackd1 if a reason to do so appears.

I am now working on a working dual-JACK prototype, in a near-production design, as a next step towards a generally transportable MultiJACK Patch Management methodology and the next big build of my Box of No Return :-)

Cheers, and thanks everyone!!!!