From my point of view, I am not sure if it is needed at this point in time.
I do not know what kind of features FACEIT is going to implement in the client, but people meet up, search for teams/parties etc. in HUBs. There is also a dedicated feature for people who are looking for teams.
This would be used by people who met in that FACEIT Discord. I do not think that people outside of it would join it to use for voice communication since everyone can make its own Discord free of charge.
Speaking of using Discord for voice communication, do you know if a lot of people prefer it over TeamSpeak/Mumble/Ventrillo or even in-game voice channel? I know that I prefer TeamSpeak myself since I think Discord used to cause random CPU usage spikes for me.
Just to make it clear, I do not mind FACEIT Discord community, but I would probably prefer to see the forums grow first. However, if FACEIT staff and community decide it is a good idea, more power to them and I will be happy to help out if needed.