While I like this being in SSRP, I really don't think it'd would work well for TTT.
TTT is obviously a team based gamemode where a lot of global communication happens at any given time. Limiting voice chat to the general proximity would make it harder for everyone to communicate, I can foresee people just grouping up together in small spaces just to be able to hear on mic which would make the map (and game) a lot more claustrophobic than it already is.