My honest thought after reading the two latest releases is this:
We know that Rysn became a Dawnshard after being imbued with a command and intent while visiting Akinah.
We also know that at some point, Wit held a Dawnshard, but no longer does.
The Dawnshards appear to be extremely powerful commands that likely require significant investiture to take advantage of (Hence Rysn being forbidden a spren bond)
Nightblood was created with a massive Breath cost, and a simple yet strong command.
My Theory: Wit/Hoid gave the Dawnshard (command) to Shashara, who awakened Nightblood uising the dawnshard command and massive amounts of investiture. i.e. The command used to awaken Nightblood was actually the Dawnshard command "destroy evil". This is why Azure's awakened sword is vastly different to Nightblood.
