Well, it looks like it could be closer than we thought, with Microsoft teasing that Rise of the Tomb Raider was running in DX12 at its Xbox Showcase Media Event. Microsoft confirmed: "DirectX 12 Showcase: Rise of the Tomb Raider, Ashes of the Singularity, King of Wushu - Square Enix, Snail, and Stardock showcased their latest DirectX 12 enhancements for Rise of the Tomb Raider, King of Wushu, and Ashes of the Singularity on Origin PCs, iBUYPOWER Revolt 2, and Maingear PCs".
They continued: "Ashes of the Singularity is taking advantage the DirectX 12 multi-adapter technology, allowing PCs to use multiple GPUs, even from different manufacturers. Rise of the Tomb Raider was playable for the first time at the Xbox Spring Showcase running DirectX 12".
We should expect Microsoft to unveil the DX12-powered patch for Rise of the Tomb Raider very soon, where I suspect we'll see it at GDC which starts on March 14.