Problem also when passing another car - especially when the other car accelerates a bit at that moment. Sometimes you just need to be able to gain a few mph quickly and with no condition.
"The driver can override the speed limit by pressing "firmly" on the accelerator."
That's what you already have to do to make an automatic downshift. Have you driven one lately that didn't do this?
If there's multiple lanes, I have NO problem leaving the cruise control on, sliding over, and letting them fiddle with their speed for a minute.
I wouldn't use this tech in the left lane though, unless it had configurable +10ish offset at highway speeds at least. And if anyone really must go variable 15+ over the posted limit, either put the siren on or add passing someone on the right to that list.