> That's for "retina" displays. I don't think there are any 8x displays right now, but probably they want to be future-proof for a while
It's kinda unreasonable to put restrictions on the users in order to achieve that. I mean, your slack team might not even be around by the time such displays are introduced. Why force the users to jump through hoops for such a silly reason? 90% of the time they're just going to resize whatever image they have in the quickest, dirtiest way to meet the system's arbitrary requirements.