Update: The show is over. I have included the highlights.

• Announcements: Elite Dangerous to make its Console Debute on the Xbox One
• "Announcing a partnership to release Elite: Dangerous on Xbox this summer. It’s a spaceflight sim that’s going to be making its console debut on the Xbox One." 
• "Microsoft wants games to be the biggest category on the Windows Store going forward....Right now, the Windows 8 store isn’t driving a lot of revenue."
• Basically we are looking at the current windows 8/windows mobile setup expande to include 10/Xbox One.
• "They will allow developers the option for cross-buy and cross-play for Xbox One/Windows 10"
• "Over the next 12 months, there’s going to be a staged rollout of all the Xbox Live features to various endpoints."
• Unreal Tournament being streamed using DX12.
  Youtube version: Removed (will look for a replacement)
• "DirectX 12 also brings big performance improvements across both CPU and GPU. Up to 50 percent CPU usage improvements."
• Direct X 12 provides 20% GPU boost only applies to the PC (Confirmed by Microsoft). Phil has said we won't see a difference on Xbox One, and he never mentioned the boost applied to the Xbox One platform.
  Update 2: The 20% boost has been confirmed to be for the PC.
  "DirectX 12: DirectX 12 enables PC developers to have a new level of power and control and is a single API developers can access across Windows devices. As shown with Fable Legends running on Unreal Engine 4, there has been a 20% improvement in performance. And as announced today, Epic is creating Unreal Tournament using Unreal Engine 4 running on DirectX 12, which sets a new bar for visual fidelity in PC gaming." 
  Source: http://news.xbox.com/2015/03/xbox-gdc-2015
  
  Update: Due to a misunderstanding caused by an interruption in the livestream, the original article mentioned that the 20% GPU improvement was on Xbox One, but Spencer did not actually explicitly mention a platform.
• "We may be seeing a return of Battletoads"
• Optional shared saves between Xbox One/Windows 10 announced
• Gigantic (Moba) announced for Xbox One and Windows 10:
  Watch trailer: https://www.youtube.com/watch?v=IJCAKJ9fz4I#t=33
  
  
• Wireless Controller will be coming to PC
• Shovel Knights to include appearance from Battletoads

Source: http://www.geekwire.com/2015/live-from-gdc-microsofts-phil-spencer-on-windows-10-and-the-future-of-games/

Watch the event: http://meerkatapp.co/geoffkeighley/27461bee-aa7f-4500-bc23-4bdb0c73c499

"Sign in with twitter" Ahahahahahahahahahahahahahahahahahahaha NO.

If you find a better alternative I'll include it in the OP.

Xbone has E.D.....LOL I couldn't resist.

This cross buy thing looks like more Xbox exclusives will be heading to Windows 10 pcs during this year.

Imo, if they really want to push the windows store on PC, bring MCC to windows after Halo 5 comes out and make it windows store exclusive! Yes, there will be a lot of rage from PC gamers but it will work in the end

This was a great showing! I really like the direction Microsoft is taking with Windows 10/Xbox One. I am glad to see Cross-buy coming to Microsoft platforms.

I also appreciate that these changes will provide indies under ID@Xbox developed with 20% more power.

EDIT: I think i read your post wrong

Dat 20% Performance Boost though! Secret Sauce revealed!

For indie games that use the free middleware (yes) they are the only ones who use id@xbox, AAA developers use more challenging and optimized methods that will still provide better performance. Generally indies use unoptimized engines, so this should be a big help for the indie scene.

Mantle itself provides better performance than D12, and you can bet that AAA developers go deeper than Mantle.