Very little is known beyond the rumour that it's going to be a tablet. This is quite a big deal - Microsoft is a quintessential software company, which is where they earn the vast bulk of their money. Even the Xbox business can be seen as a software business; for most of its lifetime, the Xbox hardware didn't make any money, with the actual games being the money makers.
As much as The New York Times adds validity to the story, it's still something I find a little hard to believe. I mean, Windows 8 is a big, big deal for the company, and it can't really afford to piss off its much-needed hardware partners at this time. As such, if there really is going to be a Microsoft tablet, I'm expecting more of a Nexus programme kind of thing, where the tablet is made by an OEM who will be a prominent part of the announcement and branding.
However, more likely, in my view, is a developer device. It's very easy to get your hands on a Windows 8 x86 device - basically any computer sold over the past few years. Windows on ARM, however, has no such luxury; at this point, it's impossible to get your hands on a Windows RT device, so it would make sense, for proper testing, to put out an unbranded developer device that developers can purchase as part of an MSDN subscription (or TechNet or whatever, I don't know the difference). Hopefully, us non-developer geeks can purchase one as well.
I simply find it very hard to believe Microsoft would give itself a major head start over other OEMs by launching their own generally available Windows 8 tablet. Windows 8 isn't expected to launch until October, and I can't imagine OEMs being very happy about having to twiddle their thumbs for four months until they can take a stab at Windows 8 tablets.
There's another a big risk involved with Microsoft launching its own tablet four months before the rest of the market does so: it will be the only device out there, incredibly visible, under heavy scrutiny and all the spotlights. If it falters, hiccups, or even just flinches, it'll be all over the press - a major dent in Windows 8's reputation even before it'd be well and good out the door.
We'll know come Monday. The same day we'll know if The Netherlands is on a plane home, or if we get a (completely undeserved) reprieve.