Details are scarce, as are available photos of this prototype, but the official name will be ヨーコ 水着でバカンスVer / Yoko Swimsuit Vacation Ver.
The source image for the figure, originally from the Yoko Artbook. There is also a companion Nia Artbook for those interested.
As the figure is scheduled for a May 2009 release, it will likely be some time before pre-orders become available.
AmiAmi did have an entry on their (Japanese only) website for this figure as of Dec. 10th JST; that page has since inexplicably gone down but the link is reproduced here in case it becomes operational again: AmiAmi.