While I do think 10M is possible, I would bet on something more like 7-9M. I think the series will have increased appeal now that Kratos is more relatable instead of being a douche. It didn't bothered me, but I think a lot of people were put off by that. It also brings a much needed refreshing to the combat, that was getting stale at this point.
A lot of people are bringing GoW: Ascension to the table. That game was released in a year where most sequels sold poorly and with the PS4 already being the new stuff. It's just like Gears Judgement. In both cases, the developers didn't want to do a full fledged sequel because that history should be reserved for the new gen game. So they were unnecessary prequels, with no important plot.
The GoW prequels added to the history, specially by answering questions about Deimos that were teased in the mainline games. But Ascension? All the Fury plot didn't add anything to the history. Don't get me wrong, I liked the game, but it is really not necessary to the general plot.