It sounds like Lemmy may have difficulty being scaled that hard, that quick. There are some database-side performance bottlenecks (that are being worked on actively) that block high concurrency and activity, as well as limitations in how websockets are being used in the current version that can cause dropouts on very active instances.

Both of those issues are being worked on, and it sounds like the websocket issue is particularly close to being ready for release-candidate. It really sounds like the focus on the dev's side is to prep for a possible reddit exodus before the blackout that many subs there are doing- meaning, get the software running reliably and performantly, knock out any low-hanging fruit, etc.