[xondono]

> So it seems like it's kind of like low-pin-count ISA-ish bus with direct pin connections to the cpu's pins.

SPI and I2C plus some generic pins. This are the typical interfaces used in microcontrollers.

If I were to build a “bigger” versions of this, I’d avoid PCIe altogether and jump to USB 3.x directly, since it’s a much better fit.