L.A. Confidential: what does Microsoft have up its sleeve?

At 3:30 on Monday afternoon, somewhere in Los Angeles, "an exclusive Microsoft media event" will take place.

Invitations (non-transferable) went out from Microsoft's PR agency, Waggener Edstrom, to the tech press on Thursday afternoon, a scant four days before the scheduled event.

That covers the who, what, and when. But the where and especially the why are still up in the air.

Microsoft says "additional information regarding the specific venue" will be sent to registered attendees on Monday morning. Until then, it's a closely guarded secret. I've booked a hotel on the Westside, close to the freeway, a short drive to Hollywood, hoping that that location will make sense on Monday morning.

The invitation concludes: "This will be a major Microsoft announcement – you will not want to miss it."

That's a pretty impressive build-up, downright Jobsian in its secrecy.

When Apple pulls this sort of stunt (which they do regularly) the company usually drops some sort of clue in the headline or the accompanying graphic. But Microsoft has offered nothing about the content of this announcement. Not the slightest hint.

So we in the tech press take wild guesses, and we talk to sources, and we try to connect the dots, as I'm about to do.

Here's what not to expect, in my opinion:

• It's almost certainly not an acquisition, of Nokia or Yammer or anyone else. That type of move requires SEC filings and usually is done via a press release and accompanying conference call with analysts.
• I don't think it's personnel-related. Yes, Steve Ballmer could announce his retirement tomorrow, and the new CEO could make his or her first public appearance. That would certainly be a shocker, but it wouldn't exactly be the kind of distraction Microsoft wants in the final runup to the launch of Windows 8.
• It's not a developer tool or an incremental update to an existing product. No one summons the media across the country for a "major announcement" and then says, "We have a new SDK." The event planner wouldn't make it back to the airport alive.
• It has nothing to do with Office or the Server and Tools Division.

So what possibilities are left? Here are my speculations:

• The location suggests an entertainment tie-in. Has Microsoft finished putting together its top-tier pay TV service to go with the Xbox Live (nee Zune) music service? If so, that would be a big deal. A Very Big Deal. After Steve Jobs supposedly told his biographer that he had "cracked the code" for the next generation of Apple TV, everyone's been waiting for Apple to deliver on that bold promise. So maybe Microsoft gets there first, with a device that's already in lots of living rooms.
• The timing hints at a full reveal for the first generation of Windows RT tablets. It's likely that Microsoft will release Windows 8 and Windows RT to manufacturing around the end of July. That's only about six weeks away. The traditional PC industry needs a few months to get its inventory together. The OEMs producing ARM-powered Windows RT tablets—an exclusive club, to be sure, with only Nvidia, Qualcomm, and TI allowed to play—have fewer such constraints. In theory, those devices could be ready to ship as soon as (or shortly after) the OS software is ready, which would mean an on-sale date in August or early September.
• Wishful thinking has some people dreaming of a Microsoft-branded tablet device, perhaps a Kindle Fire competitor or even an Xbox tablet. It's not a completely implausible idea: the Xbox 360 and the Zune players have already established precedent for the concept. If such a device were to appear, it could be sold via the Microsoft Store, online and in its small number of physical locations.
• I wouldn't be surprised to see the first glimpse of a new Xbox, with a full Metro interface that mirrors Windows 8 perfectly. Start screen instead of dashboard. Identical music and video apps on both platforms. Full SkyDrive integration. Timed to ship same day and date as Windows 8 devices.
• Tim Cook might appear onstage and announce that Apple is using its cash stockpile to acquire Microsoft and he'll be the new CEO. OK, I just threw that one in to see if you were reading or just skimming.

Or (drum roll, please): Maybe all of the above (except for the Tim Cook bit, of course).

Ina Fried (former CNET, now WSJ) is convinced the answer is behind door number three and that the Monday event will "center around Microsoft’s tablet strategy":

Sources say that Microsoft concluded that it needs its own tablet, with the company designing both the hardware and software in an effort to better compete against Apple’s strengths. Microsoft’s tablets may include machines running ARM-based processors as well as models running on traditional PC processors, sources said.

Online site The Wrap reported this evening that Microsoft will manufacture its own devices, something that AllThingsD sources have also heard in recent weeks.

I'm not so sure of that. The topic of Microsoft getting into the hardware business comes up regularly (see "Should Microsoft get into the PC hardware business?"), and channel conflicts always emerge as the top objection. But maybe Redmond has cracked the code this time around.

Whatever Microsoft unveils tomorrow, I hope it's not another big announcement of an exciting future product that won't reach customers for 4-6 months or maybe even until next year.

Announce, excite, ship. If Microsoft has learned anything from Apple, that should be the biggest takeaway.

But maybe I'm just not being imaginative enough. If you want to add to the speculation, post your comments in the Talkback section below. But make sure you do it before 3:30.

See also:

• Should Microsoft get into the PC hardware business?
• Can Microsoft pull its tablet technology together?
• What if the rumored 'Microsoft tablet' isn't a Windows tablet?
• CNET: Microsoft's mystery event in Los Angeles (live coverage)