Answer:
Sequel to a well-loved IP. That's only way possible.
That is pretty short sighted. Good developers can have a good chance at this with a new IP. Ubisoft probably managed it with watch dogs. Blizzard easily did this with hearthstone, will probably have a good chance with heroes of the storm, and I have a good feeling they will manage it with overwatch. Blizzard is great with new IPs because they don't go forward with it unless they know it is going to succeed, and they of all companies are on top of future support and additional content.
What you are actually seeing and trying to classify is how big companies who do put out the best games (I am not saying all of their games are the best, but there are no best games from small indies right now) are all sticking with current IPs. And for three good reasons too, #1 they don't want to gamble with a new IP at current finances, #2 the staff WAN'TS to continue on a specific IP, and #3 alot of IPs have been expanding on creativity and are no longer one trick ponies like GTA, Tomb Raider, and Assassins creede.
In the end, the numbers you are looking for can be easily obtained under 2 main factors, #1 is the financial bar to get in easy to obtain? (is it free? monthly cost?) and #2 is the developer team quick on updates and additional content so people don't get bored?
There are many original IPs that are F2P (just consider all the damn korean MMOs) that easily break 500k players.