I've been using it (yes, pre-release) for a few months now on an unrelated-to-FIRST website and one thing that I've definitely noticed is how much nicer it is to develop plugins for. I had specific need for a
IMAP Authentication plugin and was able to write one up very quickly by copying and editing an existing authentication class which I was able to find and figure out without needing any developer documentation. Making things even better is how it appears that upgrading versions won't require such a painful process of copying over the mods (unlike phpBB2).