Oh man, I just found out that many TVs have a built-in setting (called CEC) for controlling devices and that you can control your OSMC Raspberry Pi with your TV remote by just enabling it. I could have had a single unified remote for YEARS!

https://www.instructables.com/id/Raspberry-Pi-Remote-For-Free/

Warning from @try_osmc@twitter.com, though:

"On paper, it's great, but due to different implementations by AV equipment manufacturers, it can also cause a lot of problems."