Almost entirely a cosmetic feature, I think it’d be nice to have that granularity in customization. It’s decently common in the 40k universe for a character to take a vow of silence in atonement for something or growth towards something else, and rejects, especially those associated with ecclesiarchy, would be good fits for that.
I think it’d be a cool option for adding depth to your character or variety. Doesn’t even have to be an actually ‘mute’ option where they don’t say voicelines. There’s lots of tech in 40k that feeds thoughts to a servitor-type thing to speak for you TTS style, that could be cool too.
The latter might be safer for gameplay purposes (callouts and pinging enemies), I feel like I rarely actually hear allies say those though, as the visual ping is what alerts me.