This should have happened 4 years ago, when Alleria and Turalyon returned from Argus.
I have been saying for years that one of the two would end up leading Stormwind and the Alliance, it's just natural. They are the most grizzled war veterans the Alliance has, as they have been fighting non-stop on distant worlds for centuries.
You can expect the Alliance to be more competent now that it is no longer led by a naive little child.