Another option would be to use the Discord API to generate user tokens to actually restrict access to forum users automatically. The same can actually be done with TS as well. I have the phpBB code to do the latter and it could pretty easily be updated to do the former if it is something people are interested in.
(Specifically you would want to use this API call
and add the invite code returned to a link. TS works very similar but uses a token generation call through a telnet library.)
Auto-removal is a bit more complicated as I have a different system that handles that for my WoW guild's system (which I built the feature for), but it should be possible to extend banning/account deletion to revoke access if desired as well. Not sure when I'd have time to do it (August/Sept is very busy for me), but I could certainly share code and lend some support if anyone wants to give it a go.
If we are updating voice chat details, it's also possible to put a link that directly joins TS using the ts3server:// syntax.