No, it wouldn't be a costly waste of time at all. Because, literally, all they've done is made a few leading comments. That's it. They made leading comments at interviews that were going to be scheduled regardless and that they had to be going to...they didn't specifically organize said interviews to make these comments.
So no, it's not a costly waste of time at all. In fact, there's been absolutely NO extra cost for them to do what they've been doing on Sony's part.
And yes, it's exactly the same thing as being coy about a plot point, actors/directors do it all the time to retain a sense of mystery. And if this is a fakeout, it easily could have a point, as I illustrated in my last two posts.
Granted, I think it's likely she may die in this one, and if it's handled well I'm sure I'll enjoy it. But at the moment, I'm definitely not a fan of Harry being the one responsible, and MJ not being introduced yet. It also doesn't make a whole lot of sense to me that they seem to be building up Norman as the big bad of this series...only to have him NOT complete the one act that made his character truly iconic.