Very interesting video from Ferran together with Julia Bretos, who has insider informations about the construction and delivers some interesting numbers. You can watch this video with subtitles.
In short, around 75% of the steel-structure is finished. In total it's gonna be 20.000 tons. He predicts 100% by August 10th. 55k seats were alredy placed, around 5k remaining. The stadium could open up at Gamper at a lower capacity like 10-20k viewers to test it. He also says the club started to disassemble some services like VIP, bars etc. at the Montjuic, so they expect not to return there. More information in the video.