This is a very good bet. The "defeat device" turns out to be using a feature of the ECU platform provided by the ECU supplier. It would be surprising to find that VW was the only maker to cheat, when the cheating mechanism was available to everyone.
There are some markets, like voting machines, where requiring open, buildable, verifiable code is good practice. Cars might be another.
I was thinking of voting machines as well and think publicly verifiable code and hardware would be a good thing for cars (I don't think it's good enough for large scale elections, but that's another topic).
ps. just reading this in a post from Bruce Schneier[1] that is currently on the frontpage as well[2] which is about cheating software as used by car manufacturers and the IoT that is coming up:
Voting machines could appear to work perfectly --
except during the first Tuesday of November, when it
undetectably switches a few percent of votes from one
party's candidates to another's.
The only problem is that hardware to verify ECU code is an actual car of particular model with equipment to analyse exhaust. Or very precise mathematical model of it which would be much more expensive and would probably require super-computer to run.
There are some markets, like voting machines, where requiring open, buildable, verifiable code is good practice. Cars might be another.