well, since it has to control the functions via the mike jack, it would
have to be intigraded with the mike line at least. Basically, there would be
a jack of choice, say the RJ45, or the tradditional Round 8 pin din socket
for the microphone itself to plug into.
This would be mounted on the side of the small box that has four
switches/buttons on top for the function controls. then either a short lead
out of the box with another RJ45 or 8 pin kenwood jack on it for the radio's
microphone socket, or, perhaps a patch cable going from the box to the radio
with the appropriate connecters on it.
Depending on how flexible you wanted this particular box, the permanent lead
coming out of the box to the radio may be undesirable since you can't
lengthen or shorten it easily.  A custom made cable with the right
connecters on each end to go from the box to the radio would be more
convenient, if a little harder to build...extra jacks to solder and all
that.
Also, this box could potentially contain a balanced XLR and or TRS socket to
connect a studio microphone for better audio on air.
A quarter inch, or eigthth inch jack for connecting a foot switch, or PTT to
key the studio mike would also have to go on if I added the xlr/trs option.
You could still run a regular microphone wired with an 8 pin round, or RJ45
connecter on it into the box, or substitute it for a studio mike.

A little like the rig blaster, but much simpler and mostly designed for the
use of the function keys.
I have never seen a rigblaster of any model, and I am wondering if these
function buttons couldn't somehow be added as a modification to a
rigblaster, or if the unit is too small to accomidate extra switches or
jacks?
Also, I don't remember the dimensions of an MC60, or any of the other
popular kenwood desk mikes, So I don't know how hard it would be to add
micro switches to the bass portions of those.
If there was just enough room, these switches could be added and the other
components put inside the microphone's bass...but again, I don't have
anything to experiment with.
I know that I could probably play with an old turner plus 3 that I have and
see if the switches would fit in there just as a trial run...but I am pretty
sure that the turner plus 3 desk mike has allot more free space on the bass
between the PTT bar and the neck of the microphone, then the mc60, 60a, or
80's do.

I'll start experimenting just as soon as I can get to my favorite electronic
parts supply store and pick up some components.
73
Colin, V A6BKX