But the thing to keep in mind when you say that you still need a "clean" square wave. When it is in packetized form, the pulses are sent make up a packet, think of it like a zip file. When put together it forms a little file, the packet. Inside the packet is data such as when it was sent, what the data contains, how many packets are in the group and what number it is, as well as CRC info. Regardless of any noise, or ringing etc, if the packet does not pass the CRC check it is considered corrupt and discarded and either re-transmitted by the bus or error corrected by the DAC. This is the main difference to the bit stream, the bits must arrive at a precise point in time. But the packets can arrive whenever, as long as when assemble in the right order they are in the buffer when the DAC needs it.
As to how the DAC processes the data from the input buffer, that is up to the DAC manufacturer. Mistakes could obviously be made there, and just because the the data made it from the transport to the DAC is no guarantee that is will sound great. So all DACs will not sound the same, it's just that one piece of the puzzle we will finally be able to worry about less.
But this idea that we have been hanging onto that noise on the line, for whatever reason, can cause square sign waves to be misinterpreted is gone, if the packet does not pass the CRC check it is flagged as corrupt. I'm not saying that it doesn't happen, I'm saying that now the unit will know when it happening, and can act accordingly.