Inherit Alpha and Alpha Lock

Both function are very useful for digital painting and can speed up masking parts of the workflow significantly.
They can be found in Krita as Layer options next to layer lock.

Inherit Alpha - lets create temporary mask from alpha channel of the layer below - this eliminates the need for manually creating a mask and editing the content of it.

Alpha Lock - lets lock existing alpha channel values while enabling editing/painting RGB values

I believe both can be implemented either as nodes, node parameters or in other non-destructive manner.