I was more interested in the tuner side of things; that article
concentrates on the wired remote data.

Perhaps the serial interface has little to do with the radio operation.
From the kernel source, it seems that all the tuning, signal strength and
RDS stuff is done by the fiendishly complex SAA7705H DSP. From the block
diagram on the SAA7705H data sheet, it looks as if some dumb front-end
circuitry just hands over a chunk of spectrum, in which case the serial
port may be used for nothing more than switching the receiver, LED and
antenna on and off.