I found out about the release because my Xperia X announced the upgrade availability (I'm not using gemini as daily driver due to reliability issues - another story).
When I spotted it, there was already an announcement on the Jolla blog (blog.jolla.com) and I think it had already been mentioned on talk.maemo.org as well.
Since there's now a free demo of sfos X to download for XperiaX, and the change to X licence period, the split seems to be at the point of adding the paid-for apps now, AlienDalvik and MSExchange etc. Essentially stuff which Jolla has to pay licence fees on, AFAIUI.
I'm not usually bang up to date with all this stuff, I get most of my info from t.m.o usually.