One of cerulean studios' has actually answered this question in a comment on the blog: http://blog.trillian.im/?p=2746#comment-31043 http://blog.trillian.im/?p

One of cerulean studios' has actually answered this question in a comment on the blog: http://blog.trillian.im/?p=2746#comment-31043 http://blog.trillian.im/?p=2746#comment-31043 Mikael: Mainly inertia; we started this 10 years ago as well and have massive amounts of development energy to consider. What we lack is the peer review that a proper standard can boast, but switching to XMPP at this point would be a huge, huge project. We decided to do the next best thing (instead of doing nothing and running another walled garden), which was to publish the documentation to our protocol; we’re also going to consider building a federation layer that uses XMPP in the future. This way we get the best of XMPP in terms of federation but don’t have to throw 10 years of client and server work out the window.