According to VGC, SIE once had a similar line on its US store page for the PS4 Pro. Specifically, it read “There are currently no plans to restock this item in the future”. The line is gone now, but the sighting of something similar in a Japanese retailer reinforces the possibility that the company is phasing out the older console.
Which is a weird thing to do when PS5 stocks are still so limited. But on the flip side, even if the PS4 hardware is getting discontinued, games for it will likely still be made for a number of years more.