Re: In reality...
"The NOx problem is caused by running the engines very hot (improves fuel economy)"
There's a lot more to it than that. It's to do with the distribution of the fuel charge in the cylinder and the localised heating of the compressed air. Lots of R&D goes into trying to get this as sorted as possible. (Stratified charge being one of the big areas of contention). Computational fluid dynamics is getting better and better every year, which helps design better geometries but it also requires higher injector pressures and faster metering valve (and eventually, fast acting pneumatic/electromagnetic poppet valves)
"a 16 litre truck engine which can go from idle to max RPM and from cold to hot, each time it changes through its 24 gears in climbing from 0 to 56MPH and back between roundabouts and traffic lights"
This is Drayage work and should be replaced with a diesel-electric or diesel-hydraulic Hybrid (limited RPM range makes engine management much easier) or full EV. The engine you describe is designed and intended for long-haul transportation and shouldn't be on the roads you envisage for more than a tiny proportion of its operational life.
NOX is _only_ an issue in urban areas and even then only in the inner urban ones.
Taking London as one example, Nox is only effectively measureable within the North/South circulars and only of concern within the Inner London Ring road (and some arterial routes to the N/S circs), with small (in most cases less than 1 block long) hotspots on some suburban high streets. Even then, as of 2007 about HALF of inner London NOX was generated by static heating systems (mostly 1970s-80s era domestic gas boilers) with most of the remainder coming from large diesel engines and only about 10% from small diesels.
The same applies in most european cities.
Which means that
1: greater emissions controls on cars rapidly runs into the laws of diminishing returns
2: Paradoxically, greater emissions controls on petrol engines starts increasing their fine particulate output, so you start needing DPFs on petrol engines too.
3: Emissions controls to keep dense urban levels of pollutants down are useless and drive up costs in non-urban areas for no good reason.
NOX standards for new boilers (oil and gas) have been in place since 2001. Sooner or later there's going to be a change of rules to ban older boilers in urban areas (these are almost all unsealed systems with high CO emissions that can vent back inside the house anyway - one of these nearly killed friends of mine some time back after making them sick for years)
At some point the realisation is going to be that areas like London Zone 1 will have to effectively ban IC engines entirely and concentrate on vastly improved public transport 24*7.