I disagree entirely, the original Minecraft demos were just you spawned randomly with a chest full of wooden tools or random items but the game loop was so good that it was enough to pull me in and probably millions of other people, a simple time limited world, optional chest with tools and a hand picked seed would be enough.
The only question to me is when is a good time to introduce an updated demo? If I was Anego Studios it would be before or after a big update to stir interest in the game. The old demo is just too outdated and unappealing to be acceptable from a PR point of view. It really doesn't have to be a time sink for the devs, like i said, A time-limited seeded world with a chest of optional tools would be sufficient.
Watching something and playing is completely different, to build yourself a starter home, make your first spear and kill your first wolf is far more satisfying than watching someone else do it.