Petrol yes has the catalyst issue of enforcement rather than other technologies like CVCC Honda were utilising.
Many engines currently are ready for lean burn, its the NOx capture 3 way catalyst absorbers that are prohibatively expensive to deal with the combustion temperature resulting nitrous oxide. Its why the Mk1 Insight CVT in the states held SULEV 30 emissions, but the manual with lean burn was much more efficient but only an ULEV vehicle. That was a bit of a bonkers loss leader. The material cost currently doesnt make sense for many cars.
Diesel of course is lean by nature and indeed the focus of the the VW emissions issues, therfore in terms of aftertreatment the early 90s catalyst story is kind of irrelevant.
I can see a big push to HCCI - Homogenous Charge Compression Ignition - petrol engines, at low revs they operate on compression ignition like a diesel and offer a decent halfway house - Honda have also been working on Homogenous Lean Charge Spark Ignition, presented in 2013, that a mix of HCCI and lean burn pushing for 40% efficiency but will likely to require aftertreatment.