Maybe I am in the minority here but I often watch programs where I need the subtitles turned on for a bit and then off again, either because the accent of someone’s dialog is hard to understand (Scottish is one for example), or temporary noise level. Either way, it would be great if turning subs on and off could be quicker for eg. by long pressing one of the remote’s buttons during playback or even voice controls, although the latter I believe is reserved for Apple system wide.
I moved your post to the suggestions area. Seems like a good idea to me.
Siri controls for subtitles could be implemented, but it is up to infuse to support it. I think this would be the best approach. There are other Siri commands they can add support too.