While current Chromebooks are basically netbooks that run Chrome OS, a new generation of these devices, hitting later this year, will run on mainstream Intel Core hardware, not low-end chipsets. And the lineup of hardware makers that will be shipping these devices reads like a who's-who of Microsoft's PC maker partners. What's happening?

While I've been watching Android closely over the past few years and have come to regard that Google platform as the biggest threat Microsoft now faces—read Microsoft is Copying the Wrong Company for my latest piece about this issue—I've been unconcerned about Chrome OS. In fact, I still kind of don't quite get the point of it, and since Chrome is something that can just run on top of Android, I've never been clear on why it even exists.

Some events of the past year have caught my attention, however. First, current-generation Chromebook hardware—the devices are now made by Acer and Samsung, two of Microsoft's biggest PC maker partners, as well the comically expensive Pixel by Google—have been among the best-selling PCs on Amazon for months. Indeed, if you check out the e-tailor's Best Sellers in Laptop Computers list right now, the top two devices are Chromebooks. (HP and Lenovo also sell Chromebooks based on low-end Intel processors.)

Second, when Google announced in March that Sundar Pichai—previously responsible for Chrome and Chrome OS—would also take over the firm's Android business, I assumed a merging of the two products was inevitable. But the firm quickly stomped on such rumors and at its Google I/O 2013, it noted that there were now over 750 million active users of Chrome (presumably across Windows, Android and other platforms). And because Google "frequently serves the PC world only with web-based solutions, which will ease the transition of users away from Windows to other platforms like Google Android or Chrome," this is a huge threat. "Google wins when Microsoft loses," I added, noting that Google only graces its own Android and Apple's iOS with native apps.

Third, it's impossible to miss the fact that HTML 5 web apps are increasingly sophisticated, offering not just offline usage but also many other capabilities that we have historically associated with native OS environments. And while this distinction seems to be lost on most, when Google announced its formalized Chrome Apps platform recently—see Chrome is Going Native for the rundown—it occurred to me that Chrome-based web apps were no different, architecturally (at a high level) from HTML-based Windows Store apps running on Windows 8/RT.

Put simply, Chrome—or, more specifically, Chrome OS—has become more interesting over time, and more of a direct threat to Windows.

And this week, this threat became all the more real when Google and Intel announced that a coming set of new Chromebooks would run on Intel's next-generation "Haswell" Core processors, the same architecture that will power Windows 8.1-based PCs, Ultrabooks, tablets and other devices. Worst of all for Microsoft, two more of its PC maker partners—ASUS and Toshiba—have signed up to deliver these devices too. Acer and HP will also be shipping Intel-based Chromebooks this fall.

"NPD says Chromebooks represent 20-25% of the $300-or-less computer segment [in the United States, which is the only market NPD reports on]," Chromebook product management director Caesar Sengupta wrote in the announcement post. "In education, more than 5,000 schools have deployed Chromebooks for their students, representing more than 20% of school districts in the US."

The move to Haswell isn't super-new, in the sense that some current-gen Chromebooks run on low-end Atom and Celeron processors. But Haswell isn't the bargain basement. This is the mainstream. These devices will compete, for the first time, with real Windows laptops. (And no, the Chromebook Pixel does not count. Let's just acknowledge that this strange device sort of stands on its own.)

The most troubling aspect of this to me, and the reason I will now watch this much more closely, is that so many of Microsoft's PC maker partners—Acer, ASUS HP, Lenovo, Samsung, Toshiba—will be shipping devices that are essentially PCs by the end of 2013 ... that do not run Windows. I assume that the new Haswell-based machines will be fairly expensive—$500 to $800, or whatever—and that they will complement the low-end (and very inexpensive) devices currently in market. They will in other words represent a new front in this suddenly expanded war against Microsoft and Windows.

Was it Surface that tipped the scales in favor of any possible alternative for PC makers? After all, Chrome OS is still pretty much a joke, with very little in the way of real-world solutions that make sense for most users. But the promise is there, the web platform is strong, and the future is... well, the future is murky. Did Microsoft finally push too hard on its partners?

I'll be getting a Haswell-based Chromebook when possible—the HP looks particularly nice—and see whether the move upmarket benefits Chrome OS. I'm still not convinced. But I won't turn a blind eye to this emerging competitive threat. Neither should Microsoft.