Like I say, these concepts have been around for decades, but as you mentioned, they were phased out as the technology couldn't cope with the idea back then. Now with modern electronics, they can safely be reintroduced with far fewer reliability issues. The VW ACT takes 4 milliseconds to swith from 4 cylinders to 2.
Way back around the year 2000 I seem to remember an article about three major truck engine makers (Caterpillar, Detroit Diesel, and Cummins if I remember correctly) who were fined because their engines emitted too much NOx. As I recall it, the engines were set up for best fuel efficiency, which called for higher combustion temperatures and pressures, in turn producing too much NOx. This was well before ultra-low sulfur fuel and external emission controls.
I have heard similar things, like cars ecu's being able to detect when it's being tested in the lab so it can optimise fuel timing to make the car seem more efficient with lower emissions than you would ever get in reality. Roll on 2017 when they change the testing methods, by then every car will pay the same in road tax here (£140 per annum) so the pressure on car manufacturers to get below the 100 grams of C02 per km threshold (so Road tax is free) will be non existent.
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