Ok, so far, this is what I have understood from the lx200 structure (there is actually 22 different classes to address):
Any lx200 component class heritates from LX200Generic which derives from LX200Telescope.
LX200Telescope derives from 3 classes:
             public INDI::Telescope, public INDI::GuiderInterface, public INDI::FocuserInterface
The comment in source code says that there is "One binary for all lx200 drivers but each binary is renamed to the device name"
I have not found how this actually works but as a matter of fact, haven't found a specific binary for each lx200 class (lx200gps, lx200autostar...)

I think I will stop here for my investigation with lx200 and follow the initial suggestion from James and knro to derives from FocuserInterface and FilterInterface (took me some time to understand that FocuserWheelInterface is names FilterInterface...)
Will keep posted if this can be, and how it can be done. 

Read More...