Originally Posted by
cpach
Also an option would be Shimano Di2--you can customize what the buttons actually do, so you could set the left shifter to shift the rear cassette. If you wanted a 2x system, you could also set up the front shifting to work with auxiliary shifter buttons elsewhere on your handlebars. Not a cheap solution, mind you. Apparently you can use Shimano road shifters with an XTR MTB derailleurs for a 1x system also, you just can't mix road and mountain derailleurs. I am not an expert on Di2 so definitely do more research before you dole out Di2 kinda money, but I think it'd work.
https://fairwheelbikes.com/c/shimano...or-road-bikes/
This is a great option. I've got my Shimano Di2 certification however I have not heard that you can mix and match shifters and derailleurs. I would just stick with the road setup and just not use one of the levers. Just make sure you have waterproof plugs for the ports. Di2 is a perfect option that is gaining popularity with the adaptive cycling scene as it becomes cheaper. Shimano has even paired up with R2R which is a cycling charity for veterans.