I expect the campaign wording is to "encourage" people to get this done quickly which, if this fix is effective, will reduce warranty costs for GM and issues for customers. For those who will be keeping the car past the end of the powertrain warranty you probably should get this done quickly to minimize damage that may become catastrophic further down the road and possibly past the end of your warranty. Or you can roll the dice and try to blow a set of pistons to get a new set just before having the updates done
I would be surprised if there isn't a followup letter to owners whose VIN still shows the campaign fix hasn't been implemented, possibly with language about negative impacts upon warranty coverage if it isn't completed.
And if I owned a 2.0T I wouldn't feed it anything but premium which should be required given the fairly high base compression ratio (9.5 to 1) with FI stacked on top. Yes it will adjust for lower octane when knocking occurs but how does it know when better fuel is used? By testing through increasing timing until knocking occurs and then retarding it back to low octane tables. So I expect running regular grade fuel it is going to advance to the point of light knocking fairly regularly to "test" the fuel, there is NOT some little chemist guy living in the tank with an octane test set to tell the ECM when you change to a better grade of fuel so it has to experiment via the timing tables and knock sensors.