Wow. I went through the Instructable link. I am equal parts amazed at the ingenuity and scared by the OCD some people have at being ultralight for a PSK.

IMHO I don't see the need for anything less than a golf pencil, for the obvious reasons above, plus just sharpen the thing down to 1 inch and your good to go. Furthermore if you carry your PSK as part of a larger scheme of EDC, (like in a daily backpack or work bag) then there should be multiple writing devices in there anyway.

The hard part is finding something to write on that can be found and read. In fact, based on the ETS forum, For my hiking I ditched my grease pencil and switched to a sharpie and a 35mm tube of bright orange plastic tree tape. Write on the tape, pull apart, tie it around something for contrast and movement, move on.