Well I think you got it a little bit wrong.
If you take a look at other coins you'll see that a whole lot of them started with heavy hyping by just stating their goals, not even having the whitepaper yet. So yeah, that is a common thing, to promote your project before anything is done. The thing with the billion challenge, however, is that it aims at the people outside the crypto community who are not familiar with all the stuff we have witnessed here. With these people you actually have to get everything to work perfectly in advance. So what happens right now is @stan promotes the challenge for the local community in order to state his goals and show that bitshares is not abandoned and is having stuff going on. We get updates on the preparation process and they (regular people) will discover it when everything's ready. I am pretty sure you wouldn't prefer for @stan to go completely silent for a few months while they are working on it in order to announce their plans when all is set. That would be completely disastrous for bts, because people would think that there is no development and the project is dead.