This will most likely be like this...
However, what may happen and what i hope, is that on the contrary some development teams will still offer big boxed games on kickstarter, as it is a strong "bait" for some people and then it's likely to bring them backers who wouldn't have helped them, or paid less, if the bonuses were digital only.
In fact that's what i would have done, backing only $15 to get the steam version instead of 110 for the box...
Hey, that makes me think about something, it may be off topic but what is the most recent big boxed game you had on PC? I mean apart from CE, just a plain big box for a standard game like in the old days...
I received a big boxed copy of FEAR 2 Project Origin, ordered in Germany because it was the cheapest price at the moment and french subtitles were available on steam. I expected a regular case and when i saw that box i was like WTF :O
That was in 2009! Those germans are amazing when it comes to pc gaming.