Well...there are more differences. Optical drive (aka second bay for SDD+HDD option), memory can be upgraded to 16GB, glossy screen which IMO is easier to look at for longer periods of time than the current Air.
Nothing points to the next MBP having dual drives and having a glass screen again, so nothing is sure for now.
As for the RAM, as far as I know (somebody correct me if I'm wrong), the 4GB limit on the MBA is currently an artificial limitation that only tries to force prosumers to buy the 13" MBP which currently has a higher profit margin than the MBA.
If they consolidate the 13" MBA and MBP, I don't see why they wouldn't take your money if you want to pay extra for a 8GB/16GB RAM upgrade, unless of course they want you to buy the 15" MBP, but I'd be surprised if you had to pay 1800$ for the cheapest Mac laptop with more than 4GB of RAM.