I noticed if Flarum fails to send an email, the UI reports that the post-reply failed.
I also noticed that, once a couple people follow a discussion, posting a reply takes 4-7 seconds instead of 1-2.
I'm not sure but I think this could be related to the tasks being run at the same time.
So I thought it'd be great if Flarum borrowed the queues functionality from Laravel and allowed more "advanced" users to activate it while people with shared hosting could give it a skip.
This could increase the performance of the forum quite nicely, I think. Especially when replying to popular topics.
I'd recommend supporting Redis and AWS SQS as those are quite popular.