Chip can transmit all of the internet's traffic every second

If my math is right, you can fit 230k into about a foot, which would make an interesting cache architecture. 128k folded on the back side of the chip, 0.5 nanosecond latency.

About that, are there any modern forms of delay line memory available?

As others have said it's not the concept of DWDM that's new here. That has been around for a while. What is interesting here is that they have managed to integrate a DWDM transceiver onto a single silicon-photonic chip. As someone who has worked in similar silicon-photonic research, the challenge is to create the required filters, modulators, and demodulators that are stable enough over environmental conditions and manufacturing process variation for commercial production. Most silicon photonic structures are quite sensitive to temperature in particular.

I worked with glass fibre multiplexers that used multiple colours of might back in 2000. It's called DWDM. I moved on to different things so I don't know if it's still used, I assume so because it had no real drawbacks. But it was definitely a thing used on many expensive long distance fibres.

On the short ones it wasn't used because the equipment was more expensive than just laying more fibre.

Managing all those frequencies on a single solid state chip is the novel part here, based on my (admittedly dated) understanding.

Random test data is often used for testing telecom systems. It's valid.

Probably, they discovered how to implement the last missing part/s of such chip, so finally they could use the power of decades of moore's law to miniaturize everything into a chip.