This story also removes the [P]ackage command line option:

From the outside, 'P' creates the package in a .zip file while 'N' creates the same package in a .nupkg file. So basically their purpose is the same. I don't see a reason why we should support 2 times the same functionality. I went with .nupkg as it can contain a lot more information than just its archived content.

Also, underneath, 'P' was lacking some functionality that does 'N' does have, e.g. the zip file won't contain add-in archive files if they weren't created before.