I was able to plug my phone in at the last hotel I stayed in because its ageing 30-pin dock also had an aux plug, which my modern phone still supported. It also seemed a lot better for my device security to not give some random active device direct access to my phone.
Like the iPod itself, it's not a question of new functionality, but better usability/popularity of existing functionality. The revolutionary aspect was that you could just drop an iPod into the dock and it would start playing your music through the dock's speakers, while also charging. This didn't require the dock to be "smart", it was analog audio.
Apple's marketing is working a bit too well.
Moving the audio to all-digital moves more NRE cost to the devices. It also means there's a potential for the "choice" of rubbish DACs to save cost.
Actually, they only work when they follow the standard physical layer. Try plugging a Line device into a Mic input, or a Line device into a speaker. Or an unbalanced into a balanced jack. It'll "work" but not "correctly."
And, just like saving money with "rubbish DACs", there's room for designing complete crap, noisey audio paths (and noisey amplifiers) in products.
If people could actually agree on a standard (USB3 seems a good choice), sending audio over a digital port seems fine.
The ONLY real problem, is digital audio isn't digital audio. It's a protocol with MANY audio formats. 44Khz. 48Khz. 96, 192khz. 2 channels, 4 channels, 7.1 channels. 16-bit, 24-bit, 32-bit float. Compressed with different compressions.
THAT'S where the real shitshow happens. Because now you're basically in the oldschool Modem situation where you have to try various standards and HOPE that the sender and the receiver both have compatible formats and in failing that, falling back to some standard required format like "stereo 44Khz PCM".
Contrast this situation with digital audio, where the number of modes is exponentially larger by your own admission. Analog audio is more reliable.
This doesn't mean digital couldn't be more reliable; it's just that it hasn't typically been designed with the necessary metadata as part of the protocol.
Not smart, just have a 30pin connector. Having DAC on board would be trivial (esp. after paying the royalties for the connector). So calling it revolutionary is just being an Apple shill.
People keep building phone dock systems and they just don't really seem to take off. Maybe the best one available today is the HP Elite X3 .. running the discontinued Windows Phone.