Hmm, well I could see a female knight being passed off as a Jeanne d'Arc. That seems like it would fit the styling of the Fi?ures line.
Some more suggestions from me:
1) Tribal Warrior - I'd like to see some more with big carved wooden masks. Those are cool.
2) Crusader - This would fit and be popular for sure; it could be a different order than the Templars or Teutonic Knights for a change.
3) Demon Knight - This one could have the horned helm from the red demon knight Special Plus in another moulded colour scheme. Maybe blue and black or silver and black or something.
And, again, not that I particularly like any figures that are based on franchises or real people, but I've always thought it would be cool to make some customs based on
Avatar: The Last Airbender. A Tibetan monk or some heavy fur-coated folk (like the older ones with the igloos) could provide nice parts for these.

And some hooked swords like Jet uses would be great and could fit into the new Asian Dragonland theme probably... I'm not sure if any of you have ever watched the show.