using a cheap chinese arduino, the sky is basically the limit as to what you could do with it. based on some assistance i did with a user on subcommittee, the analog pot decoders that drive servos and the digital decoders that switch on and off switches use exactly the same protocol to transfer data over a single multiplexed channel of the transmitter/receiver link. that protocol is described completely in the article/thread posted on subpirates, with additional code bits to drive two different simple servo drivers, one i2c, and one serial. that bit of code to drive the servo drivers is all that would need to be changed for what ever purposes you intend. to properly mimic a 12+2, you will need to add cost for things like relays and other items to imitate the on/off switches (or lights), but a simple arduino should be able to drive two servos with no added hardware. i was basically doing all that extra work on my robbe fc-28 to get a total of 12 channels for extra bells and whistles on my Alvin. i figured that being able to drive servos or things that acted like servos would be the easiest to deal with, since pretty much everything you can stick on a sub these days has some type of device it plugs into, that then plugs into a servo socket on a receiver.
i have bought several items from wetronic.nl as well, and they are also good, and work as well as the original robbe parts, at less than 1/3 robbe's cost.
what types of devices does Engel recommend to use to run all the extras in the Gato? i presume they must be relays that can plug into a receiver...
