Stephen Hackett:

The question is if this is a problem for Apple. Myke isn't alone in thinking that the iPhone 6 Plus could be his only device. Clearly, there is a segment of the consumer market that may forgo buying an iPad and instead carry just the 5.5" iPhone.

Apple likely made the 6+ knowing that people who are buying it are looking at the 6+ as their main device and possibly only device.

And I have to say, it is a compelling idea. If I thought I wouldn't be annoyed everyday by the lack of pocket-ability of the 6+ I would get one.

Either way Apple knows all of this and are fine with it.