SNS
You've nailed it perfectly. There are SO many reasons to use I2S if you can, and you explained it really well. I agree that short HDMI cables are best, but I've had excellent results with the Audioquest Vodka 48 8k/10k cable at 1 meter. For small budgets, the Supra 2.1 HDMI works really well as does the Audioquest Cinammon HDMI.....but those needed to be shorter than 1 meter for best results
It is true that there is no standard for I2S pinouts, but I've never had a problem with Supra or Audioquest. Also many DACS provide pinout configuration, I know that Denafrips does in all of their DACS.
The other benefits can be true of DDCs too, as it allows for: better quality clocks, galvanic isolation, optical isolation, separating the data and clock signals, and of course keeping the I2S signal in tact from the DDC through the DAC.....with no further conversion until the Digital to analog conversion in the DAC