These are absolutely not mockups, they are in game screens, all what you see are in-game.
And for the engine, there's a couple of things we are still working on. The intro is almost done, well the text engine is done, so.. Hum what else? The rupee engine is done, sword engine is done, swimming is almost, cutting plants is done, heart is done, we are working on ''pots'' engine, etc
A demo will come soon, like in 2 weeks maybe, if all goes well, from the beggining to when Saria gives you the ocarina.