I would imagine a cautious and phased roll out. First LHR and maybe AMS followed closely by CDG, FRA and BRU.
If they all work, you could see it expanded elsewhere. I would be surprised to see it roll out across the entire network (minus the obvious leisure destinations) at once.
I would imagine they would launch it on all routes and tailor the size of the Aer Space cabin depending on the demand for it, similarly to BA's Club Europe product - if there's no demand on the route, the Aer Space cabin won't be set up. Both use economy seats, just blocking out the middle seat and putting up a curtain depending on how many are booked on to the specific flight.