I'd like to see either 768 or 1 TB become an option sooner rather than later but when do you think Apple will do it?
You can do it yourself, and get a USB 3.0 external SSD in the bargain. They work really well. I have the 480GB model in my 2012 MBA. My review is in this thread:
https://forums.macrumors.com/threads/1729071/
Lou
Although there are users who want more than 512 storage or more than 8gb of ram, my opinion is Apple will keep these as max options on the Air to keep a separation between the Air and Pro line.
I think their mentality is, anyone who needs that kind of storage or power will need a pro machine. I could be wrong and I don't necessarily agree but it's my feeling. I think anyone who is willing to pay should be able to get anything they want built into their machine.