@thomasreggi That sounds really cool.
Probably inspiration to be taken from GoToSocial (super small optimized) and Takahē (interesting job system).
Also people may not want to hear it but a multitenant/multi domain backend with shared caching of external accounts and statuses could also help scale. Takahē is heading in that direction if I understand this post correctly https://aeracode.org/2023/04/29/refactor-treat/