That's the reason why there is an 'open ecu' somewhere else in the list, most ECU's are sealed tighter than a gnats arse to avoid liability.
There has been some work on an open ECU though.
Another advantage of this would be retrofit start-stop trickery on existing cars while removing parts :)
Fuel saver as well as an emissions boost.
And I always thought it was a great name :)
I think you would seriously struggle with an open ECU. There are multiple reasons for this but the two main ones would be:
1) Manufacturers charge a ton for mechanics to use their software to acces their ECU and there is a recurring subscription charge for said software so you would be competing against a very monopolistic market.
2) Every car is drasticly different. A universal ECU would need to be a remarkable feat of engineering for it to be able to handle a honda civic as efficiently as it handles a Ford F150. Considering the amount of responsibility ECU's now hold in a vehicle, creating one which can handle parameters for all cars would be almost impossible and probably ridiculously expensive.
re (2), yes, but there is less variation than you may think
Is there though? Valve timing, fuel injection, emission control, idle. All of these factors are vastly different from vehicle to vehicle and the majority are variable dependant on how other elements of the engine are performing.
A well written piece of software would have those as presets that you could choose from a long long list of makes, models and engine codes.
Personalize the ecu to the car and you'd have an adapter problem left to deal with.
(voltage levels and pinout).
As for the spark plugs, that's true, but usually the injector rails are 'crossed' from the spark plugs so only one cylinder will actually fire.
Most starter motors are re-wound, not replaced so the manufacturers don't see a dime of the secondary market.