Taking a look at some planned releases for the PS2, there is no evidence of the new version being released for at least the next few months, if not longer. Like Lyn said, Sony seem to be too busy in other areas, manufacturing-wise..
I remember the speculation though, it was only planned to be a few MM smaller, so no big deal there, and of course the internal power supply and a slightly lesser weight. I see it as a revision of the Slimline version not a completely new version itself, so i wouldnt dwell on it too much if it does indeed never leave japanese shores...

I suppose this was a plan by Sony to re-generate the PS2 market for the last couple of years of its 'lifespan'. So, it makes sense in a way to bring out a new model. Personally i think, if one isnt brought out this year, then there wont be another PS2 model in the future.