Currently, long nicks get truncated. Ideally, the full name should be shown as well, because nicks are sometimes ambiguous. Rocket.Chat+ shows "@nick" in small letters next to the full name, which I find useful.
Maybe for the full name it would be enough to have it in the nick list (which would have both full name and nick), like konversation does. Anyhow, sorry for mixing two issues, the primary issue here was the rendering of long nicks.
Seems to work now.