John Gruber, Daring Fireball:

For most of the modern era at Apple, the company’s Mac portable lineup has been simple, dating back to Steve Jobs’s 4-square product matrix in 1998. iBooks and PowerBooks. Then, in the Intel era, plastic MacBooks and aluminum MacBook Pros. Lower-priced for consumers, higher-priced for pros.

The original MacBook Air threw a monkey wrench in this simple lineup, though. When it debuted in 2008, the MacBook Air was a premium portable, starting at $1799 with an 80 GB hard drive, and going up to $3098 for a version with a faster CPU and 64 GB of SSD storage. It was a different type of premium portable than a MacBook Pro, focused on a remarkably svelte (for the time) form factor. When Steve Jobs revealed that first MacBook Air by pulling it from a manila envelope on stage at Macworld Expo, there were gasps.

And:

This is one of those columns where I started with one idea, but in the course of writing it, drastically changed my mind. I find none of these scenarios satisfying, but I started out with the idea that the one thing Apple wouldn’t do is simply update the MacBook Air, as we know it or very similar, and just give it a retina display. I’ve been saying this for a few years now, that I saw the future as just MacBooks and MacBook Pros, and that the MacBook Air remained in the lineup only until the 12-inch MacBook could drop in price.

But the more I think about it, the more I think that something along the lines of the “just put a retina display in the MacBook Air” scenario seems the most likely.

These callouts are just snippets from an unusually long Daring Fireball column. When the MacBook Air came into being, it represented a huge change, filled a hole in the market. But the MacBook and MacBook Pro have taken advantage of the technology and material science gains MacBook Air brought to the market.

What will a new MacBook Air look like? Good question. Gruber’s take does a nice job exploring the tree of possibilities.