Note though, that the article is really about the PIO device on these SOCs', which isn't part of the main CPU at all. It's sort of a very limited programmable hardware engine for the specific task of doing PCB level interconnect using GPIO and lightly buffered streaming. In some sense it's like a thematic midpoint between an FPGA and a CPU.

It's... honestly it's just really weird. And IMHO has really, really, REALLY limited application. It's for people who would otherwise be tempted to bitbang an I2C or UART, but not for ones who can put hardware on the board themselves, or who have a FPGA handy, or even for people who want to do non-trivial stuff like QSPI displays[1] or whatnot.

Basically PIO smells like a wart to me. I genuinely don't know who wants it. Regular hackers aren't sophisticated enough to use it productively and the snobby nerds have better options.

[1] The linked article appears to be doing a quarter-VGA display in 3-bit/8-color, and is sort of right at the limit of the power of the engine.