Appledash shipping is now canon, Based on the following:
Applejack, despite being cursed by discord, is able to tell the truth when she sees rainbow dash fly off.
When applejack is mind-hax'd by twilight, the last image we see in her flash back is of her and rainbow running in the leaves
When rainbow is de-cursed, she leaps on top of applejack, not just hugging her.
I believe there is a deep emotional bond between them, that goes beyond just friends.
Even if it is never publicly acknowlaged, the effects of the relationship can still be seen.
"what our fans have joined together, let no writer rip asunder"