XMPP is huge for law enforcement and military applications. In fact XMPP is successful enough to keep updating the standard because of its penetration in that market -- even though it can't seem to make a difference in the "messenger of the day" market where it seems there was AIM, ICQ, Paltalk, Paypal, Google Chat, and Facebook Messenger which share some characteristics: (i) they don't improve over time, (ii) they don't interoperate and (iii) you will be using something else five years from now.