Things come. Things go. McLuhan's classic example of shifts in technology was the demise of the spittoon caused by the development of the typewriter and the related replacement of male clerks with female typists. It may be that the pen is going the same way due to the keyboard:

The decline of handwriting and the rise of e-mail and text messaging has been highlighted in a new survey of media consumption in the digital age. It suggests that half of written communication is by e-mail, 29% by text message and just 13% by pen and paper.

It has been some time since I wrote a letter with pen on paper and even then it was the last of a line of correspondence with someone with the purpose of maintaining the practice intentionally. Before the computer came to my house just about ten years ago I wrote at least ten letters a month to friends and family. Likely, the pen will become less common in the same way that photographic paper manufacturing has contracted and the name Penmen will live on as a cartoon or as an obscure team of soccer players in an industrial league or mid-minor college somewhere.

When did you last see an ad for a pen. I do recall Bic Click ads from the 70s causing a wave of desire amongst junior high collegues - who then discovered their ability to adjust the settings and add features to create a stink bomb.