Rumors strongly suggest Apple's Back to the Mac October event will feature the introduction of an all-new, perhaps all-different MacBook air, the first in a post-iPad world. And that has got me thinking -- how does Apple still keep it relevant?

Apple originally introduced the MacBook Air as the ultimate ultra-light, bereft of optical drive, reduced to a single USB port, yet still boasting a full-sized 13-inch screen and keyboard. Light and impossibly thin but powerful and a fully capable Mac. It was the anti-netbook.

Throughout 2008 I used a second-generation MacBook Air as my main blogging computer. I took it everywhere from my room to the coffee shop to Macworld 2009. The second generation model, with Nvidia graphics, ran Photoshop like a champ and was perhaps the best text and photo blogging machine on the market at the time.

Now we have the iPad. Also no optical drive, but without a single USB port (camera adapter notwithstanding) or hardware keyboard whatsoever. It most certainly can't run full-on Photoshop, or drag and drop between multiple windows, or maintain persistent SFTP and other connections, or do any of the million things Mac OS X excels at. But those things the iPad does do, like movies, web, email, games, books, etc. it does very well, at a much lower cost, with far more intimacy and immediacy, and with 10 hours of battery life.

Apple's ultra-portable category suddenly had two very different contenders, and that's a problem because if there's one thing Apple likes more than stunning design its simple product lines.

Upon his return to Apple it's said Steve Jobs drew a grid with only 4 boxes, portables and desktops, consumers and pro -- what's now known as MacBook and MacBook Pro, iMac and Mac Pro. It's more complicated these days, but compared to any and every other company it's still ridiculously simple and intentionally so. When you go to Apple to buy something, they don't want you confused over what you should buy. They just want you to buy it. Need portable, get portable, Need pro, get pro.

Even today while iPad has cut deeply into netbook and cheap laptop sales it doesn't seem to have hurt MacBook's much if at all. That's because iPad is a viable option compared to a $500-ish netbook or laptop. It's not a viable option compared to a $1000-plus MacBook, much less a $1500+ MacBook Air.

So what happens if Apple re-invents the Air? If it gets smaller and lighter, like the iPad, if it goes NAND Flash, like the iPad, if the price drops -- though nowhere near the iPad's -- enough to make it compelling?

Is a 11-inch MacBook air with a hardware keyboard at $1000 a viable option compared to a 7-inch iPad with multitouch? A $800-plus fully tricked out iPad 3G 64GB?

And what if Apple removed the multitouch differentiator from iPad? What if the MacBook Air got multitouch as well?

It may not this year, not if it runs OS X. OS X 10.6 Snow Leopard simply isn't built for multitouch and even if OS X 10.7 Lion is sneak previewed next week with multitouch support it probably won't reach GM status until WWDC in June, 2011, and consumers sometime thereafter. The new MacBook Air will likely ship this year in time for the holidays.

Could it be a hybrid, however? Could it run OS X but have a multitouch iOS layer on top of it? Could it have iOS come up instantly when it boots if all you want to do is surf the web, check email, watch a movie? Could it have iOS slide up, fade in, or carousel around instantly in place of the almost abandonware layers that are now Dashboard and Front Row? It sure would increase responsiveness, never mind battery life.

Think about it: iOS is what Apple has spent so much time on as of late. It was what all but bumped OS X from its traditional place at the last WWDC and it's what has been driving more and more of Apple's profits. It's even replaced OS X 10.4 Tiger on the Apple TV. Eventually, it has to move onto the Mac.

It would post some challenges -- how would a device with a fixed keyboard handle rotation to portrait mode, for example? -- but it would have definite advantages as well. Maybe not right now, but maybe by the time iOS 10.7 Lion ships later next year?

iOS comes from OS X, could it return back to that source and become the next leap forward in Apple's OS evolution? How the new MacBook Air could be relevant in a post iPad world is by being the first step in that next leap -- the first Mac to bridge the gap between iPad and MacBook.