TARDIS Exterior: The Vanilla Mushroom TARDISes
Why I went with this design: I love the idea of camouflaged TARDISes, especially with Minecraft blocks since we're in Minecraft. So I thought, "yeah, why not mushrooms".
Images: 

The idea would be that those TARDISes look like a slightly smaller version of the huge mushrooms. The door and BOTI effect would work exactly like the current Vanilla log/cobblestone/bricks exterior. Plus, I think a cool custom pre-made interior could be made for those exteriors with a mushroom/mycelium theme. (Apologies for the bad drawings. I can't model but I tried to give as many informations as possible)

I thhink it's a great idea...