3731_hero2_htc_winphone_8s_thumb_461A0730_thumb Featured Mobile This week Microsoft is releasing, to developers with apps already in the Windows Phone Marketplace, under NDA, a near final version of the Windows Phone 8 SDK (software development kit).  This is quite a departure from business as usual, where developers are encouraged to begin developing apps for a new platform well before it is released, as was done with both the Windows Phone 7 and Mango (Windows Phone 7.5) releases.

According to a post last week by Todd Brix of Microsoft announcing the SDK program, the Windows Phone 8 SDK includes a fully functional emulator that would give away new as yet unannounced features of the new platform:

I know that many of you want to know why we simply don’t publically release the full SDK now. The reason is that not all Windows Phone 8 features have been announced and our SDK includes comprehensive emulators that allow developers to test apps against a wide range of Windows Phone features. We recognize that this is a different approach to delivering tools than we’ve taken in the past. Our goal is to generate as much Windows Phone 8 excitement as possible to attract new customers when phones go on sale. This is one of many steps we’re taking to help give you what you (and we) want most.

Indeed, when an earlier version of the Windows Phone 8 SDK leaked, it revealed quite a treasure trove of new information, as we reported on at the time.

So what would be so important to keep secret that it would keep Microsoft from allowing developers to contribute new and potentially sales producing Windows Phone 8 apps?  We reported previously on speculation that the Windows Phone 8 OS itself was late, but late last week word filtered out that the OS has RTMed (note that Microsoft has not publically announced the RTM of Windows Phone 8, as they did with Windows 8 to much fanfare.  In fact, the images posted on Chinese social networking site Weibo were pulled shortly after they were made public, although we’re very sure they were authentic).

While it’s certainly possible that Microsoft has some sexy new feature they’re holding back on (and we’ll be the first to ooh and ahh if they do), a number of possibly more mundane reasons may be holding back public access to that Windows Phone 8 emulator, including:

Xbox Music

Microsoft has been keeping its successor to Zune Pass tightly under wraps, and we would be very surprised if Xbox Music wasn’t tightly integrated with Windows Phone 8.  Earlier this week we reported on rumors that Xbox Music will offer:

free-to-user advertising-funded streaming, a single tier dual subscription streaming service, a scan-and-match locker service and ALC downloads.

Unwillingness to reveal Xbox Music early (especially if the details of music licensing deals are yet to be finalized) could very well be a holdup, and with a revamped Music hub baked into the OS, it might be near impossible to show off the OS without revealing Xbox Music plans.

SkyDrive / Xbox Music Cloud Collection

Likewise, we’ve been hearing rumblings for quite some time that SkyDrive will play an important role in Microsoft’s Xbox Music plans, and some of the news from that earlier leaked SDK revolved around a setting for an “Xbox Music Cloud Collection”.  Again, an aversion to revealing this early could be a holdup.

Bing / Nokia Maps

Apple’s switch to its own mapping service has been at the top of the news this week, and Nokia has been quick to point out its expertise in mapping and location services.  In the initial Windows Phone 8 announcement, Joe Belfiore signaled that Nokia Maps will be included in Windows Phone 8:

Better maps and directions: Windows Phone 8 builds in Nokia mapping as part of the platform. Our partnership will provide more detailed maps and turn-by-turn directions in many countries, plus the ability to store maps offline on your phone so you can work with maps without a data connection.

Again, the details of this new development (including how other players like HTC and Samsung are going to take to running Nokia branded software on their devices) may not be ready to go public.

Something else, entirely?

From the earlier leaked SDK and previously announced Windows Phone 8 features, we already know a lot about what’s coming with Windows Phone 8.  Is there some major new feature we still don’t have a clue about?  Hard to believe, but Microsoft did quite successfully pull off a coup with the Microsoft Surface announcements.  Do they really have another such trick up their sleeve?

Todd Brix promised “more SDK news in the coming weeks”, and of course there’s always a possibility that news, even under NDA, will slip out, so we should know more soon.  Still, it’s highly unusual to hold back on promoting the SDK and building out an app platform as soon as possible, so what could be the holdup?  What do you think Microsoft and Windows Phone 8 is hiding?