[thinkingisfun]

"violating monotonicity means you can’t assume you’ve seen everything once you’ve read to the top of your timeline."

if that turns out to be such a problem,

1.) you can simply assume that everything fresher than 5 minutes is subject to change, so you ignore it until it's at least 5 minutes old.

2.) whatever site or app you're using could simply mark unread messages, and inform you of out-of-order messages.