So, I was running around on my toon, and having had pretty horrible gear to begin the expansion with, after hitting level 100 I quickly noticed I couldn't access heroics due to my low itemlevel. So, I started getting the gear pieces I could, starting off with a couple of quest rewards, and eventually burning my honor.
After using up about 8k honor (the honor I had and honor I farmed), I noticed my itemlevel had increase to well beyond 620 (from a starting point of <600) with just four item pieces, each of which was only supposed to be ilevel 620 -- the math didn't make sense. So, after some testing, I figured it out - if you queue for a heroic dungeon while in a pvp enviroment (Ashran for me, personally, and I guess thats the best place) so that the item level of your pvp items is scaled up to 670, the dungeon finder thinks your itemlevel is actually as high as it is with the pvp-increase enabled.
Not sure if my post makes that much sense, so I'll simplify it into steps:
1) Buy blue pvp gear (vendors are found in Ashran, by the way)
2) Put the pvp gear on, and then enter the Ashran pvp-area (as in, enter battle) to "increase" your itemlevel
3) Queue for instances
4) ???
5) Profit
Most people in mythic gear probably won't have an issue with itemlevel for heroics after leveling, but I'm thinking this might come in useful for getting alts into LFR later on.