Windows is under assault like it’s never been before, and Microsoft just missed a crucial chance to use its sweeping Windows 10-powered New Xbox One Experience update to cut a powerful new competitor off at the knees.

From the rise of mobile technology to the tremendous slowing of PC performance increases to Apple’s Mac surge, Windows has been looking wobbly for five years or more. What’s worse (for Microsoft), the titanic mistake dubbed Windows 8 sparked a mutiny of sorts inside the PC industry itself, inspiring Valve—the company behind Steam—and over a dozen PC makers to gamble on Steam Machines: radically small PCs, powered by the Linux-based SteamOS, designed both to usurp Windows’ iron-fisted control over PC gaming and to drag PC gaming into the living room.

After a long delay, the first wave of Steam Machines launched this week, alongside Valve’s radical Steam Controller and Steam Link. Make no mistake about it: The appearance of a gaming-focused, Linux-based threat to Windows, backed by the largest and most beloved company in PC gaming, is nothing short of a major threat for Windows. We found our initial week in a Steam-powered living room nothing short of intoxicating.

Zotac’s tiny Steam Machine, next to Valve’s Steam Controller.

But Steam Machines are far from perfect, as my World Beyond Windows colleague Chris Hoffman will detail tomorrow. In a nutshell, because they’re full-blown gaming PCs in their own right, Steam Machines cost as much as or more than an Xbox One—but they’re still stuck running Steam for Linux’s limited game library. In order to play your full catalog of Windows-centric Steam games, you have to stream those games from your Windows gaming PC to your Steam Machine using Valve’s slick Steam in-home streaming feature (which the $50 Steam Link basically asks as a conduit for.)

It’s a glaring potential pain point. This is where Microsoft could have struck with its New Xbox One Experience—but it failed to do so.

Leaning on its shared Windows 10 core, the Xbox One’s NXOE lets you stream your Xbox games to any Windows 10 device in your house. Critically, however, it fails to do the reverse. You can’t stream PC games from your Windows 10 system to your TV via the Xbox One, despite the fact that Steam in-home streaming and Nvidia’s GameStream technology already offer that very feature.

Nvidia’s GameStream technology already allows GeForce-equipped PCs to stream games to TVs via Nvidia’s Shield devices.

If Microsoft had enabled PC-to-Xbox One streaming in the New Xbox One Experience—which was pushed out a mere two days after the Steam Machine launch—it could’ve effectively leveraged its console to hit a major competitor where it hurts, while that competitor’s still in its infancy.

Ignoring the bare-bones Link, the cheapest Steam Machine available today costs $450. The Xbox One sells for $350. If PC-to-Xbox streaming were enabled, that $350 would grant you access to not only the full Xbox One game library, but your full PC gaming library as well. Note that I didn’t say your Steam library: While Steam Machines lock you into Valve’s ecosystem, Microsoft could theoretically open the doors to your Origin, uPlay, and locally installed games, as well.

But it didn’t. The NXOE’s game-streaming is a one-way street, and it’s pointing in a direction that does no good for PC gamers.

Mark Hachman Microsoft’s Windows 10-powered New Xbox One Experience.

Maybe the Xbox One’s weak AMD Jaguar CPU cores have issues decoding streams sent from PCs. Maybe Microsoft’s focused on maximizing the Xbox One’s utility, or perhaps it’s worried that allowing streaming from PCs could cannibalize Xbox game revenue (Steam sales are damned sweet). Arguably, that loss could be worthwhile if it staved off a threat toward Windows itself. Who knows?

For what it’s worth, Microsoft says it’s working to allow Windows 10 users to stream games to the Xbox One. Not having it ready in time to roll with the New Xbox One Experience—to shatter the Steam Machines before they get off the ground—feels like a significant miss, though. If Steam Machines rise in popularity during this holiday season, and enjoy even mild momentum in the years to come, this tardy Xbox One feature could wind up proving costly indeed.