2 channels for decoding works perfectly fine, just not duplex and the Decoding Trigger suite in Siglents permits triggering on the packets or events of interest. I've tried to find a use case where 2 channels aren't enough to decode I2C, SPI, CAN, UART and LIN, there isn't one.
so it doesn't. potentially one point for keysight
i *can* get around using 2 channels for spi (even for spi eeproms, it's not really full duplex anyway if MOSI is just there for shifting out data) and it's usually not a problem but having like analog on ch1 and data/clock on ch2/ext would be better (applies to other serial protocols as well)
no decoding on digital channels is borderline useless too, for my current use anyway