It's an odd creepy concept. If it were to be done, the pen would be ugly. I think if it was pretty solid with ashes it would look like MDF, although you could color it, it would likely still have that effect. If you scrolled the persons name into the pen, then cast the ashes into the letter holes, it would look ok. I'm not using that pen or touching it though.
There was a concept in a book I read one time, can't recall what the book was called right now but the concept was that the "soul" or something like that did not leave the body until the body was completely gone. Keep in mind this is a book..there's not necessarily truth to it, but who can really say if it could be true or not anyhow...regardless how you feel about it, the concept was that a person dies, but they are still in the body. The live in the body should it be underground for thousands of years, suffering and feeling the pain of deterioration and loneliness until the body becomes absolutely nothing. The only way to avoid this was to be cremated and blown into the wind. If you were cremated and put into an urn, well you had pain from the fire, but after the burning, the pain was gone, but you were still all together in one place to suffer eternal loneliness. You had to be spread out, preferably into the ocean where the currents would carry your dust far away from itself. Yea..creepy idea whoever wrote that. Not necessarily a concept I believe in, and not intended for any type of religious debate. Just a creepy story.