Brilliant! Some expert level Mcgyvering there! I always thought of the extra port in the shifters as just a plug for satellite shifters, but for sure, any plug on di2 works the same as another.
Buuuuut… not to poo poo on the parade, only one shifter on mtb, and no clue if there would be 2 ports. Sounds like they’ve done away with the junction boxes too. Also, can’t really hide the wires easily on mtb. Seems like “the man” wants mtb to go fully internal routing and hiding all the wires. All that said, I am more than certain shimano is already on it and they have something planned! There’s simply no way they don’t have an answer to srams newest offering. Maybe shimano gives hammerhead’s di2 integration back to sram in exchange to a little battery patent forgiveness!? Hahaha