My answer kind of depends on how hard it is and whether it is worth the effort. Personally, using a SIGHUP to do anything but (nicely) kill the process has always felt a bit wrong and like a hack for communicating. Using rc feels like the "right" way to do it.
With that said, I've never using the rc commands. I suspect it is pretty easy but the documentation always feels daunting and I haven't needed it...yet. So the SIGHUP is nice and easy.
Do you have a feel for how often this is used in mount? Do you agree with my assessment of it being a bit of an abuse of an "interput" signal to not interup? Would you even consider deprecating it? You never know what workflows will break
Until then, I will likely spend some time learning the rc interface when I have time. I spent the weekend learning about Unix Domain Sockets for my rclone credential holder so understanding the rc interface feels like a good next-step (BTW, you provided a very helpful answer when I asked about a credentials store but I wanted the excuse to learn something new so I did it my own way).