There are people working on the paperwhite support, so it should be useable soon.
However, it still remains the case that Kindle Keyboard (aka "Kindle 3") is the best/superior combination of hardware and software on an eInk device and if you need to read PDF files (presumably scientific ones, formatted for A4 paper size?) then the best device to use is Kindle DXG. So, if you own both Kindle 3 and DXG then you are perfectly well equipped for many years to come, assuming that the technology moves at the same slow pace as it did since 1970, i.e. nothing really worthwhile happened in computer industry since 1970s except Unix, TeX and Linux (and its derivatives like Android).