Not trying to be rude here.

But i can't understand any of that. 

The industry needs more new blood and more ideas. This big franchises have shined and burned too early. In one gen, CoD is going to be substitued for other FPS like Titanfall and Destiny (and Splatoon if we're lucky). AC won't survive more than this gen, it won't be an AC in the 9th.

You trust the pre-order charts too much. They aren't very accurate.

I'd be surprised if it didn't outsell Black Flag on X1 and PS4, overall is tricky given less platforms and isn't there a PS3 / 360 separate Assassin Creed title coming?

I actually think it might have some impact. I mean the majority of Assassin's Creed players are on PS4. The PS4 have to date sold more then double(almost 1 million more) of what the XboxOne version have done at retail.

Right now it's been marked with only the XboxOne version but I think it will pick up the closer we get to the release date and more of the "casual" players get to know that it's multiplatform.

What would that change? Wouldn't matter when they bring them out, they'll still be the same. Unless you're talking about people being fatigued by the series.