Hm.
You can actually download all of those provinces in user mods (Balansegeng, for instance, and I think the original mod is something like African Expansion). I'm assuming they actually bought the rights to those mods from users (which is awesome, in a way), because it looks EXACTLY like AE, but that does make me wonder why I'd pay for something that's technically free already.
What I'm really wondering, though, is how this is really different from playing as Christians/Pagans. I mean, did they improve the Jihad somehow? Did they add additional Muslim-only events? I want to know what I'm getting that I can't just download via the usermod forum, because from what I saw in the video, I've already pretty much got all of that via mods (added traits, the African expansion, etc), and hell, you can already turn Muslim characters on with some *very* simple tinkering.
That said, I will be buying this if there's anything I can't get for free already. I didn't get the ruler mod thing just because I though it was silly and unnecessary (and again, basically free if you can mod even a little bit), but if they're offering something with even a little original content and functionality, it's worth it to support them. IMHO this is easily the best game of 2012 so far by a longshot.