Private messages are pretty much a core part of every significant social media system.
Also pretty much a core part of PeakD. And extremely easy to integrate into any Hive frontend. Or indeed, any website. But people seem reluctant to use our very own PeakD Chat. Which is a shame, as it works perfectly for community and personal messages.
Weirdly, I have never seen any objections to it. Or reasons why it is not suitable. Only a distinct lack of interest. But I will continue to check it daily in the hope that it takes off.
!BBH