Diggles are intelligent, and social. They lay eggs. They live underground
What are their temperment?
"if Gaslight Games isn't terribly concerned about defining the minutae of Diggles, I don't think they would object to Toady imply making things up"
If they are ill defined then they are a terrible inclusion.
They arn't the Jabberwocks where they were intentionally ill defined so that they could be anything.
They are ill defined because they are a standard RPG monster. Heck they seem like a reference to the Prinny given their appearance and general stature.
In order to fit in the game the Diggles need to be defined, they need to fit within the game and the context of the world. In a mod that is easier but this is the base game. Remember the Diggles do not work the way the game defines as well (which is intentional) meaning that to function you also have to redefine the diggles and alter them.
It's an Easter Egg, not a documentary. If Gaslamp says it's fine to easter egg diggles, they will either provide the information Toady needs, or they will let Toady make it up to fit his world. Arguing that you cannot add a FANTASY creature to a game because you don't know what it REALLY is, seems just a bit, err, silly.
The only important questions here are whether or not Toady is interested in doing it, and if so, is Gaslamp Games willing to allow it.
Everything else is trivial and meaningless as an argument because if an agreement is made, Gaslamp Games will either give Toady the information he needs, or Toady will make it up.
The whole purpose of the thread here is to introduce the idea. It Toady likes it, and Gaslamp likes it, it will be pathetically trivial to make it work without impacting Dwarf fortress in any significant manner.