Will that drive down the general price? I heard for Gen IV Toyota will hope to produce the ones for the US in the US...
The US is not generally considered cheap labor. At one point the Blue Springs MS plant was going to assemble the Prius, but those plans changed. Toyota Motor Manufacturing, Mississippi, Inc. (TMMMS)
Japan recently decided to join the fiscal Quantitative Easing crowd like US and EU. This is expected to devalue the yen which could make Prii from Japan, cheaper here. On the other hand, USA is the main country asking for Plug_in cars to be developed and we have been giving gov't support to companies who set up plants in USA. So it makes some sense to do it here.
IMO, the bulk of the cost for the plug-in feature is the battery. Toyota doesn't make the lithium battery so I doubt there will be any significant savings by producing the PiP domestically.