It is a question that will be debated until the end of time: just how many players is the ideal when it comes to co-op games? Eight? Four? According to Infinity Ward, it's just two (yeah right). If you ask Microsoft, they are thinking a wee bit bigger. Like, many orders of magnitude bigger.
Don't believe us? A recent Microsoft job posting mentions qualifications including "building a backend capable of hosting a 300,000 player game in real-time". Almost a third of a million people, all playing at the same time? It's almost unimaginable. Our minds are blown just thinking about it!