They're probably in pre-production, if anything is happening at all.
They have to:
- budget and find financing (this was probably started by the time they announced it, but maybe not. It's not uncommon to announce a film before you've secured backing).
- write a script, which will involve edits, changes adding scenes, removing scenes, storyboarding, etc.
- put together a full production team, hire designers & crew, start designing, approve the designs, schedule the building of sets, hire effects people (practical effects, digital effects, lights, sound...) and schedule principal photography and post-production.
- audition and cast hundreds of people; dozens of principle actors and supporting parts (the speaking roles), and extras (usually done through independent extras casting agencies).
- scout locations and book studios.
I'm sure I'm forgetting a few elements, but those are some of the big things, and there are dozens of little things as well, like catering, contract negotiations, riders, Local IATSI negotiations, permits, clearances for footage and music (not just of Queen), you name it.
Personally, I'm not expecting to hear much from this production until it's done, unlike The Hobbit movies, Harry Potter or a Star Wars film, where there are behind the scenes web documentaries and video journals and such.