It's funny how people can interpret the same report completely differently but when I read about the Test Track rehab, all I got from it was that there would be some re-theming to promote Chevy products. I didn't get any sense that they'd be changing the actual physical ride and certainly not that it would become just a simulator. I'm not sure why some of the podcast crew thought that. It still says you will board a 6-passenger vehicle, same as now, and take the car out on the track. So my expectation is that the ride will be the same but the video and back story may change.
Someone from Disney called it a "simulator", and everyone thought it was going to be transformed into something like those "mini-Star Tours" at malls, etc., since what they described sounded a lot like a design-and-ride system like Sum Of All Thrills.
Test Track *IS* a simulator now though.
What seems certain is this:
1) Pre-ride queue will be rethemed, getting away from the "vehicle testing" theme, more to a vehicle design theme. I will be GLAD when the extremely repetitive noises are gone
2) Vehicle design stations will be somewhere - possibly where the theater rooms are at, but I'd think they'd need a lot of them.
3) Somehow these designs transfer to the ride. How different guests' designs who end up in the same vehicle will be resolved is unknown.
4) The ride will be modified in unknown ways to reflect the design decisions of the guests. And hopefully the ride mechanism is improved to be more reliable
5) The post-ride area will be even more like a car showroom than it is now...and more heavily biased towards the Chevy nameplate, if not exclusively Chevy.
Overall, I don't think the ride experience will change much, at least for the outside portion. Inside could be rethemed (again, to get away from the testing theme), but probably not differ significantly as far as the track is concerned.