The API is provided to the upper layers as a hardware abstraction layer. It shields the application (enigma + plugins) from the complexities of the supported underlying hardware).
An abstraction API is explicitly NOT something that returns a simple data structure that the code deals with directly. If you have that in mind (you are clearly not alone then), you've missed the entire point.
The main point here is "abstraction". Which means that code should NEVER make any logic decisions on whatever data is returned, that (string) data is for display purposes only. If this design rule isn't followed, and the functionality of code depends on the (format of) data returned, the entire abstraction is pointless.
This implies that there should be a governing body that manages and versions the API, on behave of all teams, to make sure the API provides the functionality each team needs.
For example, ATV wants to know if a box has RCA audio output. So the API needs a "hasRCAAudio" method, returning a boolean. They should not have to resort the all the code currently in the SystemInfo's of this world, that should all be removed.
The same is true for all interaction with the hardware. For example, to interact with the box LED, don't access proc entries, but call API->setMainLED(0...100) (i.e. a percentage). It is then up to the abstraction layer to deal with the value passed. It can be ignored or throw an exception (box doesn't have a LED), converted to a binary value (box only knows on and off), or used to control the intensity.
The calling code (enigma or plugin) shouldn't be bothered with how this works, or even if this works, it is hidden in the abstraction layer.
It is the task of the governing body (to give an example) to decide whether or not the aforementioned method ignores the call or throws an error. If it throws an error, it probably also needs a hasFrontLED() or something.
The API is not something simple, a one-time thing, it will constantly evolve, and it needs governing to ensure compatibility for all teams involved.