Hello Dave, nice work by the way again ... ^^
I am wondering, why not use a Lipo (much more compact and or higher capacity) with a boost with dc linear regulator after that ? If needed a very low noise, use capacitor multiplier circuit. Very handy to kill noise. You could fill the battery with a regular phone charger. It's kinda fast ... That could be nice. I don't know if this is more eco friendly to buy lipo once or buy AA and throw them away ...
I am not a big fan of all integrated DMM chipsets, or dual chipsets solutions. Why not use a 24-32bit Delta sigma dac ?
The arm is quite nice. I would be great that the software could be tweakable or opensource for community updates

. I know this is a hardware product from a manufacturer, but I am ready to pay for "hobbyst" (and good) DMM that I can tweak a bit. Or it would nice if it's sold like the fluke kit too

I am quite intrested by the bluetooth function. If that function works well with a laptop & ready to python scripts that would be great

... If the beast don't power off all the time

Good luck to you in this Adventure Dave.
I am thinking about a product that could be handy myself. Unfortunatly in my country open a company is quite a challenge ... way too much bloody documents and taxes ...