Minecart with Dispenser

Minecarts with Dispenser are an unimplemented vehicle that, as the name implies, are minecarts with a dispenser in it.

Other than the screenshot tweeted by Dinnerbone, no detail about its use, function, or activation method were published.

In 1.5, it was made possible to put any block in a minecart by editing NBT tags. Dinnerbone was possibly demonstrating that functionality with the dispenser cart.