It won't be a separate cabin with a curtain divider - if it was then APD would be doubled. It's all to do with the takeover/merger (however it is described) into IAG as OneWorld members must have a European "business" offering. This is simply the way round it - differentiation between those in cattle class and those not - middle seat and free refreshments - thats it!
Was planed regardless of OW and IAG.
It sounds like that would be hard to manage onboard though without some kind of divide. Unless EI make it so that someone on Aer Space can sit in, for example, rows 1-6 and those without Aer Space in 6 onwards but that still means there are technically 2 different cabins onboard with 2 levels of service.
Like someone suggested earlier. I could buy the cheapest ticket going and someone else may decide to buy the highest Aer Space fare. Without separate cabins, If that person sits next to me then we both get the benefit as their fare ensures no one next to them. They don't need to call it Business but much like every other Euro Carrier I've seen, Aer Space is essentially business class. Same seats as Y class, middle seat blocked and free catering.
It will be row specific so no confusion.