In short, this is possible to do... (that's what I just read @TheZag)
..but folks choose not too.
I totally agree that minor changes or corrections to overpowered sets might not be applicable.
That said, 'revamps' could absolutely be considered.
This could be a great way to skirt the cottage rule guideline.
Each reason you listed to not do it could be flipped around.
Many of the revamps already come with new powers or changed power names.
How would you choose? I trust Homecoming to use good judgement and their willingness to listen to reasonable feedback.
"I know it when I see it" -Supreme Court justice Potter Stewart
Given that less and less folks participate in development, this is a fair request which could be considered.
It might help with many scenarios:
Players who take a break to come back to wildly different characters that they've invested time into.
Players who don't feel heard in the open Beta process because they were too late in the cycle.
Player could play both versions and decide for themselves which they prefer.
Changes to Regen could be possible without impacting the many who like Regen with a tweak versus the idea of a total revamp in order to chase the meta or some maniacal vision of what Regen should be.
"not all sets have to be the same" -Troo
Cottage Rule.
Dark Armor.
Consider this: If the new Force Field sets are so great and such improvements who cares if someone chooses to play the old version? Play how you want.
Give players options.