For what it's worth Tesla has been limiting how fast older models are able to charge at superchargers, with the stated goal of extending battery longevity. I guess there's some truth to the stated goal, but I imagine it was more about nudging people to start charging at home. The affected models happen to be a lot of those with unlimited supercharging.

I think the offer they've made is a decent one. Looking at my charging habits I would actually have preferred the $5k rebate over 6 years of supercharging. I wouldn't want to spend 30 minutes every week at supercharger, and charging over-night at home is dirt cheap.