I'm still thinking the most satisfying solution to consumers is the one with the least impact to them. And the least impact would be to let people who own, (and are happy with), these cars, continue to drive them.
The downside is the amount of pollution above what was advertised. There are so many sources of pollution, could VW pay for measures to reduce an amount of pollution equivalent to the amount above what they advertised? Improved scrubbers on coal powered electrical plants? Industrial heaters/boilers?
I'm looking for a way VW can address the extra emissions without affecting current owners. I suppose it's been considered. Just haven't heard anything about it.