Seems like there are several groups working on a fantasy version of Impetus - there are several posts on a fantasy version at the Impetus forums; here is another site in Italian about fantasy Impetus; and AONeil has started one at his web site.
I have a few ideas also, especially towards using Tékumel as the background. One would be a simple addition to the roll for unit damage if the affected unit has steel armor. Steel armor is a big improvement on Tékumel, since the planet tends to be metal-poor.
I do want to keep the modifications for my version of fantasy Impetus to a minimum, though.