If anything I think we actually know a bit more about F.L.Y. than Taron this time in 2015. We knew nothing about Taron's trains or restraints until they did their reveal week.
From the Vekoma Factory and test set up we have seen the trains (albeit unthemed), the seats and restraints, the curved launch track parts and the prototype rotating seats in action - thanks
@mrrc
Construction is progressing exactly as intended. They're making good progress and I'm certain they'll get it finished for summer 2019 as planned no problem. The long construction period is necessary (there is literally no other way to deliver a project on such a scale) and I'm sure no one (Vekoma certainly aren't) other than impatient enthusiasts are bothered by it.
EDIT: Some views from the carousel, through the gap where the former monorail used to go, of the theming being worked on in that corner.
ANOTHER EDIT!:
There is a rather tall new support with two sections of new track attached. The tallest is travelling slightly upwards after coming out of the Zero-G and the lower bit comes out of the helix next to Maus.
The support for the flying position track directly after the highest point of the lifthill has been erected. It can be seen in this video from the test set up.
No sign of the lifthill itself yet but they seem to continuing with concrete walls around where it will be, and in front of the new support a steel structure (a building possibly) is being erected. Presumably the lifthill will be fully enclosed.