-
Obviously totally doable if you like craft and dodgy hacks, it’s a derailleur we are talking about, not an MRI scanner.
But why would you?
Isn’t an electronic system with sealed motor the reason we don’t want cable actuated systems anymore?
Even worst the cable is pulled by a motor that requires a power source not compatible with the rest of the system.
Breso-
But why would you?
The advantage to my eyes is that you could do 8-speed electronic, or upgrade your 11-speed stuff to 12-speed with just a new cassette and chain, or replace your derailleur for £20 instead of £100, or whatever.
If you've got 10-speed Di2 and want to switch to 11-speed you have to buy a whole new bunch of parts. IMO that is because of planned obsolescence and greed and nothing else; I'm 99% sure that they could have upgraded them to 11-speed through firmware alone. In fact they used to work on 11-speed before Shimano disabled it. How likely is it that current 11-speed eTap is going to work with 12-speed stuff? Not a chance in hell.
frankenbike
Someone's gonna crack it or come up with an open source alternative any day. Shimano and SRAM are going to cry when people get crappy old derailleurs working with 12+ speed for £50.
the simpleton's version would be this:
https://www.youtube.com/watch?v=RYgaulRbll0
tell it what derailleur you've got (whereupon it looks up pull ratio in a database) and what speed cassette (whereupon it sets the sprocket pitch). Just like a Rohbox.
or:
https://www.youtube.com/watch?v=MEMDepeSEUA
https://www.youtube.com/watch?v=ThED8L_tjb8