After going through the state of Linux distributions handling SecureBoot, UEFI-guru Matthew Garrett confirmed via his blog that Linux on the Microsoft Surface is likely a lemon.
The challenge with loading Linux (or any non-Microsoft operating system) on the new ARM-based tablet is that while it implements UEFI SecureBoot, it doesn't have the "Microsoft Windows UEFI Driver Publisher" key. This is the key used to sign Windows drivers and other non-Microsoft software (e.g. the signed Linux UEFI boot-loaders). Microsoft meanwhile has its own private key and this is the only UEFI SecureBoot key present on the Surface. Without the Surface having the "Microsoft Windows UEFI Driver Publisher" standard key, it's simply not a matter of having OS boot-loader be signed already to have support for this tablet. Microsoft only wants its OS on their tablet.
The Microsoft Surface tablet is based upon NVIDIA's Tegra 3 (T30) SoC with quad-core ARM Cortex-A9 1.3GHz processor, 2GB of RAM, storage capacities of 32GB or 64GB, and runs the Windows RT operating system. Being based upon the common NVIDIA Tegra 3 SoC, the hardware itself isn't too attractive or unique. You can already find plenty of other Tegra 3 tablets on the market capable of running Android/Linux like the ASUS Eee Pad Transformer Prime, Google Nexus 7, Lenovo IdeaPad Yoga 11, and NVIDIA's Cardhu reference tablet.
As Matthew mentions in his post, loading Linux or any other operating system to this first-generation ARM-based Microsoft Surface tablet would likely involve finding a vulnerability within the device's firmware in order to execute arbitrary code.