While referral traffic is probably mostly people using Reddit as a store of knowledge, doing things like site:reddit.com searches on Google, not principally use-Reddit-as-a-forum users, one does imagine that trying to require users to use Reddit logged-in will probably cause more users to leave Reddit. This is probably an opportunity for the Threadiverse to pick up refugee users from Reddit. Might be good to simplify and smooth the path for new Threadiverse users as best as possible, since I imagine this'll probably be the last "big moment" with potential friction for Reddit users in getting Reddit users over the hump to using a walled garden.

Reddit will start testing the login requirement in “select,” non-US markets in Q4. The company will use those tests to decide what a logged-in-only Reddit will look like “globally,” per Huffman.

It won't be all at once, then; Reddit will probably want to assess what how severe the impact on userbase is, how many people they can convert to using their app or having a login, and what tactics will work best in converting those users. So one might expect influx of new Threadiverse users over time as Reddit gradually shifts regions to being login-only.