It's not been impossible to get a MacBook Air with 8GB before now: since 2012 you've been able to upgrade for an additional $100. But that's a 10% surcharge for something that's almost essential for modern computing -- just having a few too many Chrome tabs open in El Capitan is enough to choke a 4GB machine. The upgrade should keep the Air relevant for a few more years.
Of course, there's still the issue of that screen to contend with. When Apple upgraded it to 1,440 x 900 in 2010 (the original Air had a 1,280 x 800 display), that was a respectable resolution. When taken together with the color balance and viewing angles, it was seen as a great package. But a lot's changed in six years. Apple's more recent laptops all have "Retina" displays that almost double the Air's resolution. Only the ultra-budget (for Apple, at least) 11-inch MacBook Air and the all-but-forgotten non-Retina MacBook Pro offer inferior displays.
With the RAM upgrade a near-necessity, the Macbook Air has been uncomfortably close -- $1,099 vs. $1,299 -- to the 13-inch MacBook Pro, a computer that offers more power, a better display and only weighs a pound more. Now that the MacBook Air comes with 8GB of RAM, there's a little more breathing room between the various models in Apple's laptop lineup. You have the 11-inch MacBook Air at $899, the 13-inch at $999. The 13-inch MacBook Pro and the 12-inch MacBook at $1,299 and finally the 15-inch MacBook Pro at $1,999. Everything just makes a little more sense, and all that's left to fix now is that display.
Unfortunately, it seems pretty unlikely that Apple will ever upgrade the 13-inch MacBook Air's resolution. More probable is that the aforementioned (and today upgraded) 12-inch MacBook will get cheaper over the coming months and years. Once Apple gets the asking price down to three figures, the MacBook Air range will have little reason to exist, and Apple might finally retire what many people believe is its best laptop ever.