In servers with a large number of members, being able to scroll through the offline member list in general chat is not a feature valuable enough to warrant the drop in performance. However, there are still negative effects of the current behavior. One of the most prominent effects is that when in a channel which very few members of the server are able to see, let's say 20 or fewer - the offline member list is still hidden. This can make managing a staff team difficult at times - it's easy to even forget that someone has access to a channel, as they can simply set themselves as offline and remain constantly invisible. This is equally the case in channels that are only visible to a small group of people, and can make the task of definitively finding out, as a user, who else has access to the channel near impossible.
- Difficult to determine who has access to a channel. This effect can mean that users have permissions where they shouldn't, simply because administrative staff aren't aware of it.
- When a Member is offline, updating the roles of that Member can be awkward. You would have to rely on finding their latest message or using the clumsy member search in server settings.
- When a Member is offline, and you need to speak to them, you would have to go through the same steps to be able to open a DM with them.
- Generally unappealing to see a completely empty member list.
My solution to this is that offline members are hidden on a per-channel basis, not on a per-guild basis. Each role should have a cached property "large" (which @everyone gains when the server becomes large), where if any "large" role has read access to a channel, offline members are hidden. The large property of roles would be determined based on the number of members that have the role. I assume that this behavior would not cause a drop in performance of clients, since the primary issue is rendering rather than simply the number of members. In an ideal world, offline members would not be hidden at all, but this would patch up the primary issues associated with it.