There was loose but compelling evidence Sony has quietly started winding down PSPgo yesterday, starting with the very basic of steps: ending production. Neither Sony in Japan nor America had made public comments about the story, but Andriasang has since noticed Japanese audio visual website Phileweb heard from Sony that PSPgo production is over. Further sales will come from existing stock.
Sony's official website makes the future of PSPgo pretty clear, with hardware listings straight up saying (in the red Kanji text over there in the corner--we double-checked) PSPgo shipments and sales have stopped.
I've contacted Sony Computer Entertainment America regarding a similar status for PSPgo in North America (which is likely), but the company has yet to respond. That itself, however, says something.
You can still purchase PSPgo from various places online, including Sony's North American store, but the time is ticking, folks.