OK…frankly new info for me. Thanks.
Historically, Iwakuni has had one of the better relationships between the base and local Japanese community so it probably made sense to move more personnel there from that perspective when the Japanese government started looking for a location for the move.
The Japanese literally tore down a mountain in Yamaguchi prefecture a short way away, loaded it onto a conveyor belt to barges and dumped it into the ocean next to the base. It was pretty interesting to watch when I was there. Allegedly, the Js figured all the ways they Eff'd up the Osaka Kansai project and incorporated changes into the Iwakuni construction that will alleviate the sinking issue.
IIRC the plan was to push the flight line east and build up more supporting infrastructure to support the influx of population where the current flight line is. Since the late 90's/ early 2000's Iwakuni has seen a lot of new construction (New PX, and food court area, New Chap... err recreation building (since the GOJ won't pay for the construction of religious buildings) and a Tri-Club to replace the old O, E and Staff NCO clubs). A very large portion of the construction and reclamation costs are being footed by the Japanese so urgency to complete the plan tends to waiver and delay with the recovery of the Japanese economy. In the early 2000's it was supposed to be completed in the not so distant future, but as the years have gone by (and Japanese govt priorities have shifted) it seems like it's become more of a back burner issue, especially since the Japanese lost entire communities of their own that they have to rebuild as a result of the tsunami, but there is still discussion of it happening eventually. I haven't heard any "firm" dates for the move. Maybe some current FDNF guys would know.
(looking it up it was apparently supposed to be next year but was pushed to 2017- what that means realistically? Who knows... allegedly the Yuts are moving their resident Herk squadron from Oki on up as well.
http://en.wikipedia.org/wiki/Marine_Corps_Air_Station_Iwakuni)