Drove by on Sunday, February 9. The rest stop is closed.
At the time I had not checked online, but the timeline is actually quite well defined, though disappointing. There's a page detailing the steps https://www.a6-rubigen-spiez.ch/a6/de/thun-sued--spiez/rastplatz-buchholz
The rest stop should re-open around March 2027. The concept images on the website show the Fastned canopy (funnily, with no chargers underneath). If the concept images are accurate, only 4 charging spots are planned. I assume the pictures are for the west area but maybe both will be a mirror image.
There are webcams, including one above the rest stop. Maybe we will be able to follow the construction of the Fastned station on there https://www.a6-rubigen-spiez.ch/a6/de/webcams