This isn't like the old days. Considering the internet will do a lot of promotion for them, I think I'd rather they spent their effort on getting the full game released as soon as they're able to - It seems they're just polishing it up.
Perhaps a demo could be a later thing to help promote their game after release if they so choose (
KSP and
ETS2 were sold to me in this way), but it'd be a little silly to prioritise that first for the sake of nostalgia.