Holy crap, talk about over engineered and cool. The Richard Mille RMS05 Fountain Pen (£83,000):
http://www.richardmille.com/watch/rms05/
"The movement is based on a skeletonised baseplate and bridges made of grade 5 titanium. This mechanical heart with 12 jewels powers a captivating display of mechanised kinematics that releases the white gold nib. The push-button at the end of the pen triggers the baguette movement fitted with a recoil escapement and a barrel. This escapement, traditionally used in striking watches, releases the head of the nib within seconds in one harmonious mechanical motion.
...
Replacing the cap raises the barrel in a fraction of second via a complex mechanism running through the body of the pen. At the very same moment, the nib delicately retracts, ready to emerge again at the merest touch of the push-button. The pen’s creators also worked on an ingenious method of removing the nib to insert an ink cartridge without damaging the smooth functioning of the mechanism and the pen."
http://en.worldtempus.com/article/new-watches/sihh-2016-richard-mille-rms05-foutain-pen-2452812