What voltage/resistance standards would be required to satisfy potential members?
1. Characterized 10V standard based of LM399 for DCV (over 20-40C ambient temp, over 12-20VDC input)
2. Characterized 10K standard based on hermetic foil or wirewound resistor for OHM (over 20-40C ambient temp, over 1-10mA current)
3. Perhaps 1mA current source based of same LM399 as self-check point
However this would not help to calibrate most of the meters other than 3458A, so it's rather only for base range check.
What are the pitfalls?
Few : Shipping cost. Module can be made small, but still would be 40-80$ to ship internationally.
Risk of loosing the package. Also frequent shipping back is required to make sure reference still agree to original values.
Would the outcome be better than no calibration (current situation for many)?
If one after absolute accuracy - yes, of course it would be better.
If just need ratio measurements - not so much.
But perhaps it's less useful for more popular 6.5-digit DMM owners, because even for simple check you need 1V,10V,100V,1kV/10ohm-1Meg in decades, not just 10V/10KOhm.
The idea is that 10 people pool an amount of money sufficient to calibrate and adjust one of the members' high end DMM (say a HP 3458A)
I'd skip on this idea, and modify it into "few members that already own calibrated reference meter help to check travelling reference box". Not much would like to pay for calibration of someone's meter with unknown outcome, as this "club program" would be a long-term thing, not a "all done in one month".
I can jump in and help, but will need exact and defines conditions of such activity to be ran, so it would be helpful.
Ideally I can see this as next path:
A. Design and build few pieces of "Travel-box" with DCV,OHM reference in it and perhaps Raspberry Pi Zero with EEPROM to store measurement data/temperature/environment condition and test member name.
B. Send it to well-known volt-nut "A" to calibrate for DCV,OHM reference value over temperature range
C. Assign measured data to box
D. Send it to club members "A" -> "B" -> "C" -> "D" -> "E" -> "F". Set hold time e.g. 2 weeks for each member, so it would take 5 months for 5 members to loop a reference (2 wks shipping, 2 wks test)
E. Last member "F" sends unit back to "A" to recheck and recalibrate if required. Deviation and delta of each member data would be recorded
F. Repeat cycle again.