Its a loose, loose - you focus on the launch date, you get the retail and media lined up behind it, get the conversation going, buy the adspace and so forth -
So when do you ship the backers physical copies? The answer is - late, because if you ship them early - you get diluted interest, potential customers that arent happy they are excluded, people talking about the content of the game early...
And when you ship them late, you enrage the superfans, because - why should they be the ones waiting, and so forth...
You could release digital first - but retail wouldnt like it.
And thats not even the primary reason - depending on your release strategy you want to create buzz. Everyone talking about, that "it will be available tomorrow". Not "did you get yours in the mail today" discussions.
Also - you dont want to dilute the price point - which is exactly what most Kickstarter backers would want to. They are Day 1 customers who would probably spent 20-30 USD extra to get goodies. At what point do you cannibalize potential double purchases - and at 60 USD listprice plus 5 USD merchandise, plus shipping - where is your profit margin? The PC version simply would launch at a cheeper pricepoint.
And would you want the discussion about why the PS4 tier suddently is 120 USD?
And then you dont have a publisher yet (afaik) - and Sony "only pressing the Blurays - for a different publisher", nope - thats not happening.
It is hard to even find one reason, why you should even consider it. The people who are asking for it now are the same ones who would buy it as a collectors edition on launch. They are very much value conscious.