Is it possible to do an operation on all layers/all visible layers automatically?

For now I would like to save all layers to separate png-images but later on I would like to perform different tasks.

In Gimp i use a script to save out all layers. I'm trying to find out if I can change from Gimp to Krita for my image editing.

No, that function/script doesn't exist yet.

Too bad.
Perhaps it could be done by an extension?
How would one do do write an extension? Could you point me to some documentation on this?

Good question... Actually, most of it is in place already in the scripting plugin. But the scripting plugin got in disrepair. The code is in krita/plugins/extensions. It uses kross to bind to the Krita objects: http://techbase.kde.org/Development/Languages/Kross.

Another option is to write an extension in C++. The imagesplit extension could be a good example.