From the leaked emulator we already know Windows Phone supports 2K (double 1080P) screen resolutions.
Now a new entry in the GFXBench site suggests that such a device may already be under testing.
According to Gfxbench.com somewhere a Qualcomm processor running a Windows OS is testing a cropped screen with a 1422 x 800 screen resolution. The setup was powered by the Adreno 420 GPU, which is at present married to the Snapdragon 805 processor, and which supports a full 4K resolution.
Of course the entry could related to Windows RT, but it would be significant if Microsoft intends to keep up with the specs race after all and release a handset with monster specs some time this year.