What if a mod that allows some mods, that need a plugin/mod on server to work, to have a separated server that can connect client directly to each others, even in servers that doesn't support it (exemple, Simple Voice Chat on vanilla server, you just need SVC and the mod I suggest to be able to hear everyone that got those 2 mods, even on unsuported servers like purely vanilla ones)
#Clients server mod connectors
vague lake
mystic temple
Each mod would need manually adding support. For simple voice chat it shouldn't be too hard as it already uses a separate network connection anyway. You just have to make it connect to an exernal server