... read the whole story at dev.to.
Good question. This is actually more about product evolution than it is about scale. Right now, we've built our product to, more or less, scale to any possible number of users. It leverages shared cached resources a lot. But as we evolve, we're trending more towards personalization. Even just the current user's profile on the home page was a product evolution that could potentially degrade the user experience.
As we add more features like this we trend in the direction where it could make sense to distribute our data. At some point, this will be easier than managing our current solution. That's when this sort of thing will make it into the app.