[dzaima]

This might not sound entirely awful in theory, but I'm fairly certain it'd be entirely awful in practice for a good amount of users.

Having colored backgrounds might look ugly and thus immediately make that a non-option, and, even if viable, are still problematic if new messages are added while reading, as you'd need multiple colors for the reading pass the user's on.

Having to click a button repeatedly is also likely to be entirely unacceptable UX for most users, never mind that you're essentially recreating the receive-order message list, just without displaying it in a sanely traversable format.

This problem is hard enough with linearly added messages to the end, making it 10x worse is awful.

[dzaima]

And then there's the issue on switching between clients (e.g. PC and phone) or otherwise having client state lost - if the complete reading progress isn't saved server-side, then it becomes entirely impossible to restart reading; whereas with a receive-order log you can at least manually scroll to the message you read last and continue downwards.

That said, a similar problem already exists with edits, and a universal solution for arbitrary insertion should also be able to improve arbitrary edit notifications.