When opening the properties of a Discord channel, then going to the Members tab, the members are listed by Discord username and channel display name. There is a Name search box above the Members list which has the simple prompt "Name".

As a user, I expected a search to match on both the username and the server nickname. However, it only matches on the username, which can be odd when people mention members who they commonly only see as the nickname in the default client (while in Ripcord, the username is bold and most easily-remembered).

Not a bad idea, but unlikely to be implemented anytime soon. Marking as deferred to move it off of the open issues.