if you look at the web:
https://www.google.com/search?q=iges+vs+step
http://thatcadguy.blogspot.it/2012/12/step-vs-iges-or-why-step-is-better.html
you get some tips
when I decided to develop the exporter the options were:
kicad IgesUp
kicad StepUp
then the rest is just code 