I think Fundamentalism would be a good government for Civ4, but it will probably fall prey to "PC" - political correctness. Perhaps it might be seen as related to the Osama-Terror-Muslim complex and dropped due to PC.
Anyways, this government should be seen without ideological prejudices or assumptions. It should just be a different and interesting concept.
For example, I love C3C Communism. Democracy is the government I would never choose in any Civ3 game, yet in real life most of us would want to live in a Democracy.
I would like to see fundamentalism implemented as a type of Government, as I wish many more viable and diverse governments featuring different strengths and balancing weaknesses for Civ4.
This is of course difficult to do, but I usually go Monarchy OR Republic and later Communism or stay in Republic.
I simply never have any use for Facism and Feudalism! Even more so for Democracy, I NEVER use it!!! Republic beats it hands down.