Duncan's pretty much got it, and Rust's summary is good too.
Characters are created according to a set of cats-iron guidelines, so GM vetting shouldn't take too long, and all characters begin from a common frame. There will be guidelines too, for GMs, so that moderation will again have a common framework that should ensure reasonable balance irrespective of geography.
At present, my thinking is that the whole of Glorantha will be covered by the metaplots (and there will be several), which tie into already published works, like Blood of Orlanth, Dara Happa Stirs and the forthcoming Pavis Rises. I do agree that feedback into these metaplots may be tricky, but feedback will be evaluated based on the nature of the scenario and its importance to the metaplots. Some major scenarios will only be run once, which will limit the possible effect of plot inflation, but the details on how it will work are still under discussion.
But it should result in, as Duncan notes, far more adventuring material that GMs can use, within or without the Living Glorantha framework, for their campaigns.
I'm looking forward to it. Its going to bring the kind of dimension to Glorantha that we saw during the 90s Renaissance when there was a distinct frisson between what Tales of the Reaching Moon was doing and AH's work when Ken Rolston was developing Gloranthan supplements.