PolicyService is designed chiefly for the Global Compliance System right now, it has no bearing on the allowed links policies. A game feature to return information for a player for tailoring game features does not contradict standing rules on links.
AllowedExternalLinkReferences is still just a reference table based on the Social Media links allowed on the tab: there has been no such word about lifting the ban action on Discord. It is not allowed in games, regardless of whether or not PolicyService returns it in AllowedExternalLinkReferences.
In regards to links that are allowed in games or features integrating third party platforms (e.g. Twitter promotion or Twitter promotional codes), this table can be used to toggle those features.
I answered this same question some days ago:
You can also view some discussion here:
https://devforum.roblox.com/t/using-policyservice-to-determine-if-you-can-show-a-discord-invite-to-a-user/517172
Wait for official response from Roblox or contact Developer Relations about the matter if you really want something concrete from Roblox. Otherwise, keep Discord links off your games.