Edit:
Also I didn't say they should abandon Kalimdor. But I think there would be much more room for interesting conflict and good old savagery if we saw some radical group of Night Elf terrorise the Horde in Ashenvale, instead of Tyrande and the regular army being involved. They couldn't do that without causing another war, and now that Sylvanas is out and a bunch of nice people are in charge of the Horde, I fail to see how the Alliance would want to continue waging war over Ashenvale.
Just bring in those SoD Night Elves and everything works out.