mr 134a, you sound like a government paid engineer type. That is a compliment.
I seem to remember a few years ago, someone on THIS SITE tried exactly what you originally described. They converted a system to 134a and it worked.
I did a search, and I cannot find it. Maybe the mods deleted it when one of their computers crashed.
I don't like POE oil ! ! ! and I would welcome ANYTHING that will bring back the OLD mineral oil. Unfortunately r134a will NOT accomplish that.
I have wondered what other refrigerant could be used that the INSIDERS/lawmakers will NOT declare dangerous, or OFFENSIVE to THEIR CAUSE...
My 2 cents......