it's actually more complicated than you guys think.
the transition from iphone 4/3 to the 5 was fairly simple as only a single dimension (height) has changed (from 480pts to 568pts).
however, with the 6 and 6+, stuff are different.
there are 2 different issues there:
1. iphones 4/4s/5/5c/5s and the new 6 have the same screen dpi, and therefore share the same assets (i.e. @2x). however, the 6 has a different width/height size which means you need to rethink the entire layout of the app and you can't just replace the assets with bigger ones (as they are the same assets, unless you start placing code for each asset saying if iphone 4x/5x use asset X, if iphone 6 use asset Y).
2. on iphone 6+ you have to deal with two issues: a. higher res assets (i.e. @3x) and b. a 4th screen size.
so basically for every screen in the app you now have 4 layouts: iphone 4/5/6/6+ and two sets of assets (@2x and @3x) where previously we just had a single set of assets (@2x) and 2 layouts which are very similar.
my point - it's going to take more time than it took devs to support the iphone 5. (but yes, most big companies will support it within a month, now that we have all the technical info.)