They need to announce Stretch Goal 5 ASAP if they want to get people interested enough in it to start throwing their money at the computer screen.
They have been curiously slow about some updates, and I'm not sure why as I imagine if they, say, doubled or tripled their update frequency (by doing one whenever a goal is met, and whenever a goal is announced, and whenever a midpoint is reached, or something like that) they would probably bump up total pledges by a good 10% or 20% just through increased exposure and so on.
Perhaps the 1.8M stretch goal is the last thing they really
want to add to the project. Particularly considering their target release window.
As it stands, it looks probable they will hit 1.8M on Thursday. Of course, there's normally a fairly big rush at the end of a high-profile KS, and if they want to capitalize on that they'll need a fairly interesting stretch goal #5, since #4 will basically be in the bag there.
Very interesting stuff.