WinRT "Play To" with non-certified DLNA devices
I just discovered this from a link on the Microsoft Answers forum, and thought I'd pass it along (it works perfectly on both my Surface RT and Pro to an uncertified Samsung TV.)
Basically, only Microsoft-certified playback renderers are allowed to receive DLNA Play To codfntent from a WinRT application. You can Play To uncertified devices on the desktop, but there you're limited to MP4 and WMV video. In a WinRT app, applications can use any of their media content to send to a certified receiver. That means that in mobile.HD for example, you can use the Devices charm to send MKV content over DLNA.
This registry edit, though, will let you send content from WinRT apps to even non-certified devices: http://blogs.msmvps.com/connectedhome/2013/03/30/using-uncertified-play-to-devices-on-surface-rt-w8-apps/
I realize this is probably old news to some, but I just discovered it and figured it would help others here too. Now just to wait for 8.1's Miracast support, and Microsoft might actually be able to compete with Airplay finally. :D