If all the polygroups became stretched and and even more concerning; corrupted, does this sound like a reasonable instant fix?

If you've been using polygroup UVs and you have a finished sculpt use the character as a morph on a new CC3 Character to get fresh non corrupted & uniform UVs.

I don't know how the Reallusion morph tool works but if it can bake the new shape with proper uniform UVs then perhaps the developers need to script in the GoZ returning to CC3: "apply Modified Zbrush character as a morph on a new fresh CC3 to clean up any UV inconsistencies and bake."
Perhaps UV issues could be auto detected and then this pops up as a potential fix.

I've listened to other people on the forum frustrated about the UVs being stretched after major sculpting.

This method could potentially fix 6 problems "superior visual results-no stretching", "we get to use polygroups!", " no UV errors -we get to use polygroups!", "dummy proof UV accidents/unwrapping", "time-faster creations" and "less user problems = less need for customer support" so really it's a win/win.

I marked this as a bug -the polygroup issue had originally come up long ago -not initially announced in the GoZ plugin sale but rather in the forums as an unexpected Zbrush pipeline annoyance to the workflow. They did at least tell us not to change any vertices when exporting at least.