The only time Remedy has been really long making a game is Alan wake and the original max payne, when doing max payne 2, it was a 2 year dev cycle.
but what have remedy been doing since 2010?. Remedy started very early work on max payne in 1996 after they shipped death rally, and they begin thinking about alan wake in 2003 after max payne 2.
So it makes sence that they started thinking about quantum break shortly after alan wake.
Max payne took 4 years for it land since conception,Alan wake is there only game that took a ridiculously long time since conception.
and you have to remember with Alan wake they showed one trailer of it and then we didnt really year much for years. Also alan wake went through many changes it was originally an open world game, and the Microsoft partnership would have slowed things down a bit.
With quantum break its different, they have been firmly aligned with MS or years now and were planning using the Xbox one from the very start of development (with dev kits mind you), so a smoother development process should occur.
http://youtu.be/gxb_75Z1h-k?t=4m29s
In this interview he states
there out of pre production hence in production for at least a year, they could of been in production for even longer! he just stated that they they are not long in pre -prod and are in production he did state how long for, they could of been in production for 6 month before that interview.
With it been in production for at least a year and the fact they have shown some gameplay snippets I think fall 2014 is defo possible, its very un Microsoft to show vidocs with little gameplay segments and have the devs talk about the gameplay and game as a whole when a game has years until it lands.
I'am calling a fall 2014 launch, going with my gut.