Rack gear was out of bounds.  However, I can use same concept with smaller Midisport (I have 2×2 & 4×4).  They can be stuck just about any place.

On midisports, you have to connect to PC to use patch bay mode.  So, I just
use Thru.  Whatever goes into 1 comes out all 8.  So, info is
distributed via assigned channels.  But, this also means you can't use
Omni on devices.  You must manage your channels.  This is true of all
midisports.  I use a 4X 4 to run Axe Edit, Triaxis Editor, FactorLib and
Swtchblade GUIs.

So, for me, this looks like the perfect
solution.  I wouldn't need a splitter, just a merge box.  This solves
the TF/MF challenge.  But, now that you've suggested setting tempo on
GCP, I'm hooked. I need to come up with a way to make that work for other devices
too.   I want tempo to be universal.  So, I am thinking that I now need
one more step: a way to "distribute" tempo CC from GCP to all channels
on 8×8, 4X4, 2×2…

I'm thinking: Run midi from GCP into something that will
XMT Omni, then to Midisport so every channel gets tempo.  I'm not sure
if this is possible.  But,obviously, we all have multiple devices that require clock/ tap tempo.  I have at least 6.  It would be excellent to have one source (IE GCP) of tap for all so I don't have all these tap sources.  Most devices can accommodate this w/ midi thru.  That may suffice if set up correctly.