Developing?
I don’t think it’s that far yet.
https://www.webmd.com/vaccines/covid-19-vaccine/vaccine-passport-covid (March 11, 2021)
“The U.S. doesn’t have digital vaccine passports yet, but President Joe Biden has issued an executive order that asks federal agencies to look into the possibility.”
As long is this is just theoretical.
Mull / weigh / consider = commie talk for threatening action that has not yet taken place.
“Working to develop a standard” = still just theoretical.