User blog comment:MisterWoodhouse/Social Activity, the 2010 Editor, and Unpausing Migrations/@comment-26483202-20200929184937/@comment-26339491-20200930235615

You're not entirely wrong there. The vast majority of wikis doesn't use talk pages, they use message wall, where notifications have worked for a long time - but there are several very large and active communities that do use talk pages and that will rely on having notifications for them on the UCP. We'd only noticed recently that this fell under the table because we haven't had large, active wikis on the UCP that used talk pages until we started migrating big communities. Now that we've recognized that oversight, we're working on fixing it. You should see talk page notifications come live within days.