I think it's safe to say that until someone actually has had their car fixed by this new software, and then tested its performance and consumption after that we can assume that it's impossible. I'll believe it's possible when I see it.
My guess: VW europe will claim to make a performance-neutral fix, but simply cut the performance and increase the consumption of the affected cars. Anyone in the EU who finds that annoying can try to scream with very little chance of getting any compensation from VW because of how EU consumer laws work.
In the US where they are actually scared of being sued into compensating customers they will make more advanced fixes potentially even retrofitting urea systems where possible.