Ferrrry Eeeenterestink !!
I posted my latest query here ~4 days back AFTER emailing the Canonical folks asking how to get & use ESM.
Neither effort has brought me any new info.
The absence of more info seems to point out that nobody here has tried this to keep 18.04.x, AND - that Canonical really cannot be bothered to help out users who may wish to throw money at them in the interests of continuity.
As Mr. Spock was known to say:
Fascinating.