Unfortunately the news related to XMPP aren't that huge...
> Improved XMPP support
Just really means that the support of the XMPP protocol was improved. There are no new functionalities just yet (but there is this open RFC: https://notabug.org/diogo/gnu-social/issues/21
Key changes are:
XMPPHP library modernization: https://notabug.org/diogo/gnu-social/commit/3290227b50582ed29790f0bb10210362ca2f4093
XMPP Plugin faulty regex bug fix: https://notabug.org/diogo/gnu-social/commit/e0887220b0ac97a7abce1e70652c6727c16cfe3d