Not knowing anything about the engine, I can still offer opinions...
I'm unsure of how Cadillac handled the valve train on their old modulated
displacement effort... I do know there were solenoids mounted under the
valve covers, but that's about it.
With the current state of the art regarding engine controls, a workable
modulated displacement engine is getting pretty close to "do-able", though I
would have reservations about longevity.
One of the benefits of the much touted 42 volt system (that is always
promised but never delivered), would be solenoids powerful enough to operate
poppet valves (like the intake and exhaust valves in our motors). So, this
mystery auto maker may have a 42 volt system on the go.... or, they may be
using techology from HEUI diesel engines. The Ford PowerStroke diesels
utilize high voltage for injector operation... the old 7.3 works at 115
volts supplied to the injectors and the 6.0 uses 48 volts to the same end.
There is no end to some of the amazing things that have been tried with the
infernal (sp) combustion engine. In the early 80s, Ford had bought the
rights to the "poly-motor".... built largely of space age plastics, this 4
cylinder twin overhead cam engine weighed something like 175 pounds and
delivered (IIRC) 170 horsepower. Ford Motorsports was also hinting of a
ceramic pistoned 1.6 litre four cylinder.... bragging about (again IIRC)
I recall an article on a SAAB engine... I can't recall if the goal was
modulated displacement or modulated compression ratios. The engine was built
similar to the old Offenhauser engines.... the cylinder was cast as part of
the head. In the SAAB effort, the position of the cylinder head was raised
and lowered in relation to the crankshaft.
Even back in the late 50 and early 60s, manufacturers were experimenting....
Chrysler with it's free psiton gas turbine.
Much of the groundwork, though, has been laid out by independants.... Smokey
Yunick (God rest his soul - he's kind of a personal hero) spent quite some
time developing his "stratified charge" system... This engine utilized a
turbocharger.. but not as a power adder. It was used to "homogenize" the
intake charge which was, as I recall, a very lean mixture.
When it comes to the internal combustion motor... if you can dream it, there
is probably someone playing with one in his "secret garage". Thanks for
being a captive audience.