Actually those tutorials are on wiki, but not everyone is reading wiki, and on the other hand there is very little documentation on how to do all this magic with editor, you can see around, custom nodes, custom pins on blueprint functions, custom displays for custom data types etc.
Here are two tutorials I have written about this subject so far:
Custom K2 Nodes:
Custom pins on blueprints:
More things to come, as I work on extending editor and learn something useful.