The catch up for BS, in theory, should only cause some price parity with old world ores. If Ghost Iron price goes up high enough, most (smart) people will just continue to use old world ore to level, only throwing in Ghost Iron when it's cheaper. In other words, this particular thing can't drive prices much higher than other ores. Best case scenario everyone uses it to circumvent Fel Iron and the price goes that high for a short while.
The crafted PvP gear shouldn't be in super high demand IMO. People who were playing in 5.1 already have it just from honor. The only people I see buying much of it are leveling alts, but they were most likely the same people buying the old crafted gear.
The legendary quest will be the real driver IMO. 20 trillium bars per character that gets that far in the legendary quest. That's 200 ghost iron bars (realistically more like 170-180 counting the proc rate). You also have to factor in the new epic recipes. That means more living steel demand, which in turn means even more trillium demand, which in turn means more pressure on Ghost Iron Bars. Also the new bar, Living Steel Ingot, takes 10 ghost iron bars as well.
http://ptr.wowdb.com/spells/138885-dragonmaw-reborn for instance, is going to take 15 Living Steel Ingot and 8 Living steel in total. Which is (15*10)+(8*6*10)=630 Ghost Iron Bars to make ignoring transmute procs.
So yeah, Ghost iron should go up, but I don't think the "catch up" will be the main driving force. Though I do expect that to keep the price high into the forseeable future (including into future expansions).