User blog comment:MisterWoodhouse/Profile and Message Wall on the Unified Community Platform/@comment-1333424-20200305183231/@comment-37336800-20200305212732

User Talk is going to exist separately from Message Walls as they do now, without any changes except those made by upgrading to a new MediaWiki version.

User talk will presumably still be toggleable in Special:WikiFeatures. If the wiki's administrators decide to opt for User Talk instead of Message Walls they'll likely be able to flip the switch and have it done.