[LAU] How to get a persistent midi instrument source port? ( lightweight )

[hgn]

Dear list,

to avoid the https://en.wikipedia.org/wiki/XY_problem I'm going to tell 
you my goal first, then my current route to a solution, with a missing 
piece.

I work with several midi instruments. Some of them USB, some of them 
DIN, all of them have different names. Only ever one is connected at 
once.
I want my programs to accept data entry from my instruments, no matter 
which of them is plugged in.

What is the easiest way to do this?

My current idea is to establish a virtual jack midi thru port. All 
software can use this port as midi data source.

Hardware instruments then get be connected via one of the many 
auto-connector solutions: The one built into QJackCtl or 
https://github.com/SpotlightKid/jack-matchmaker , which is what I am 
using already.

The virtual jack midi port is the missing piece.
What is the best way to get one? "Best" means least resources, least 
administration overhead.  E.g. any answer involving the words "plugin 
host" is already too much. Ideal would be a simple daemon program I can 
autorun after starting jack (with qjackctl script-after-start)

So I am either looking for that midi thru port or a different solution 
that works even better.

-hgn

P.S.
In case the JACK devs are reading:
AFAIK Jack works under the assumption that audio System out 1 and 2 are 
the main abstracted stereo outputs and are available on any system. This 
leads to great portability across all systems.

I consider midi data entry with a single instrument an equally typical 
use case and would like to propose to add a single midi thru port to 
JACK directly. No more, no less, nothing to configure, nothing to check 
for as user or developer.