The Mage does say that learning to create a portal to somewhere you have never been is extremely difficult, and very dangerous. He knows how to make portals, he just doesn't know how to make a portal back to Avaloren, which is why he focuses on his theory of using the memory of living things.
Also, his research was all destroyed, so there are probably a bunch of complicated formulas that would need to be made from scratch.
It would create more urgency, certainly. But the Arathi are still locked in combat with the Nerubians, and I imagine they would do all in their power to go to the Beledar if it wasn't for that.
Once we get to 11.0.5 I imagine Anduin will tell the Arathi about his theories on the Beledar, which will give them renewed energy.