I received an email from the hotel after my original booking had to be cancelled:
As promised, I’m reaching you out with some news from SO/ Paris.I am happy to inform you that the official opening of the hotel is going to be on the 6th of September!
Before that, starting from August 1st , we are preopening our hotel for our first guests to have an exclusive sneak preview of our property.
The restaurant will have only hotel guests and the ambience in general will be more quiet but you will be able to discover our brand new establishment before anyone else does.
Otherwise, our doors are widely open after September 6th and you are welcome to come any time after that to fully enjoy SO/ Paris experience.
Please let me know when you look for an accommodation in Paris and I will be happy to send you our best offer.
As I have no plans to go to Paris in August, I won't be able to join this "sneak preview", but if anyone here is interested, I can forward the contact.