It’s come up in discussion several times and I contacted Quick Charge Corp for advice.
They now offer a “special order” octopus charger MB1210X6 at $586 (3 week build time) which has 6 individual 12V 10A circuits so that you could charge each battery individually rather than 6 in series at 72V. Theoretically this would prevent the need for battery overcharging just to boast one of the weaker batteries in the string.
Al