The iPhone 6+ is currently being treated as a mobile device.
This is because the thresholds for window.innerWidth and
window.innerHeight are 414px by 736px

Currently we invoke tablet mode only when one of those values is over 768px.

It's hard to get an idea of the sort of traffic we get from iPhone 6+
as it doesn't have its own unique user agent.

I looked on James's iPhone 6 and I can confirm that the site generally
renders well on it in tablet mode. Once strange thing I noticed
however is that if in landscape mode, clicking edit gives you the
option of VisualEditor however if you click edit in portrait mode you
get wikitext editor with no VE option. When in landscape mode and
switching to portrait mode, you stay in VisualEditor but the interface
becomes too cluttered. We'd need to make some optimisations to the
toolbar in conjunction to enabling tablet mode on an iPhone 6+

See http://imgur.com/JsOOM2K to see how it currently looks in portrait mode.

Proposed actions:
* Optimise the text 'Editing' next to the title in VE mobile mode

* Optimise the VE toolbar for display on a 320px screen - I would
suggest hiding the bold and italic buttons via media queries

* Drop threshold from 768px to 736px