I am very, very curious about how much this will cost. People have this mindset of downloadable indie titles being $15 - or maybe $20 - regardless of any factors around the game's development (and, to be fair, you shouldn't have to know anything about a game's development history). This game, though, strikes me as a game that should cost more than that, both because of the amount of content that is apparently in there, as well as the cost to create it.
If anyone remembers the Shovel Knight sales/budget breakdown, the very loose budget estimate is $10,000/person/month. The last time I looked at the website for The Witness (the site is down right now), there were ten people working on it, although they haven't all been there the whole time, and some of them may be part time. I don't know when the game went into full production, but for ease of calculations, let's say it's been in full production for five years. Using that budget estimate, the game will have cost $6,000,000 (although I bet it's significantly more than that).
I have no idea how many copies the game will sell. Shovel Knight (which I'm not saying is comparable, but at least it's a number) sold 180,000-ish in its first month (I'm not sure if that includes Kickstarter sales). If The Witness costs $20 and sells 200,000 copies, that would be $4,000,000 before the cut taken by Valve, Sony, and Apple (which I believe is 30%).
My ultimate point is that I wouldn't be surprised if this game costs $30 or $40, and if it's more than $20, I'm really curious about how people will react.