Nice! Just upgraded. Seems to be working well.
I had some trouble with the nicknames extension. I had to remove it from composer.json, then upgrade to beta 15, and then install nicknames afterward. Not sure what caused it, but it seemed like there were some compatibility issuers with fof: user-bio, best answer, sitemap and one other I am forgetting... Strangely, Composer seems to be happy with them coexisting with Nicknames after previously upgrading to beta 15, then adding Nicknames. Hopefully, someone else finds this useful.
One thing about the Nicknames extension, and I'm not sure where to post this: Should there be an option to set Nickname when signing up? E.g. click a box "would you like a nickname different than your username used to login?" and then a new textbox appears.