Recently XMPP has got some extensions, mainly Message Carbons (XEP-0280) and Messages Archive Management (XEP-0313), which make it already quite competitive to some non-free messengers like Skype etc. These extensions are supported on newer jabber server side (ejabberd&prodigy) and in several clients.
However, in Linux, the situation is not that good. All these new XMPP extensions seem to be fully supported only in Gajim (https://gajim.org/). Pidgin has experimental patches, but they are not incorporated into main branch.
In KaoS we have telepathy-gabble, but the development of it has stopped in 2014. Other options are Pidgin and Thunderbird, but none of them support these XEP's.
Could Gajim be considered to be added in KaOS as a best functional Linux XMPP client?
I know, it needs quite a lot of python packages, but there seems to be no better choice...