Pretty interesting how long Zoroastrianism survived, despite the incredible oppression they had to deal with. They were ruled by Sunnis for most of the period, so presumably weren't people of the book (so third class citizens rather than second class). It would be interesting if there was a little bit more in terms of dynamics between religions in general, hopefully they'll find a way to add in more than just war, conquest, and conversion.
Actually, Zoroastrians (as well as many other religious peoples including Hindus and Buddhists) were occasionally considered "People of the book" despite the fact that they were not (well, technically not "People of the Book" but "Dhimmi" which was the classification for non-Muslim subjects who were given a special/protected status). Basically, the fact that it was easier to rule people you were simply taxing a bit more heavily over-came the fact that it went against the rules of scripture. Wikipedia talks about this under the article on Dhimmi, check it out.