What alloys can be used to make a metal pencil like this one?
"Silverpoint" nibs have a long history in art and significantly predate modern drawing tools such as the lead pencil (made of graphite and clay but possibly called lead as lead metal was one possible material in metal pens). Silverpoint writing and drawing doesn't smudge or fade and many examples have survived almost unchanged over hundreds of years.
There is a useful site with a good history of the original artistic uses of silverpoint pens here. According to this site a wide variety of metals will work. Historically which was used depended on status:
It seems tht many metals will work. The dictionary of Art is quoted as saying:
The current preferred metal for artistic use seems to be fairly pure silver.
The silverpoint.com web site sells ready made points of both silver and gold.
It isn't obvious what metal or alloy is used in the pens mentioned in the Wired story, but it isn't silver. It apparently contains at least some lead as the pencils come with warnings not to let children chew them!
I actually make metalpoint pencils and use pure lead for the writing material. It's obviously a bit toxic (because lead), though I'm experimenting with making custom lead alloys (possibly with a percentage of bismuth, as I have some laying around) to reduce the overall lead content. In terms of utility, however, pure lead leaves a reasonably dark and easy-to-make mark.