One-off retail/download purchase, with free-to-play style microtransactions would probably be the route they take on consoles.
MW3, the 'unsuccessful' CoD, did 15m on Xbox.
Anyway, if The Elder Scrolls Online shifted 6m, it would be a success, granted. The problem is on console, how do you monetize it, as someone else mentioned on the last page? Subscription? On top of Xbox Live Gold? No trade in value for the '2 weeks and it's gone' brigade? Can't see it being as big a success as Skyrim, and it needs to be bigger, much bigger to support the maintenance, hosting, patching etc etc etc infrastructure.