This message was on the minecraft forums homepage about 13W02A:
A Note on Textures
Starting from this snapshot and forward, blocks and items will no longer load their artwork from one big sheet of sprites. Instead, they’ll have individual files for each image they’re using. The benefit from this is that it will be easier for Mojang to support custom blocks and items in the future. It will also allow Mojang to mix and match block artwork resolutions, and make sure that you get graphics for blocks that your current texture pack isn't updated for. Pretty awesome!
That means porting will be much easier. Now, tell, what texture pack would you guys port now?