Platinum Era :
It's going to start with online subscripton and over time slowly become F2P, look at Star Wars: The Old Republic for example
SWTOR when F2P because it was heading towards a disaster as a subscription based MMO due to it's troubled launch. Had SWTOR been a successful MMO it would still be a subscription based MMO today.
I should actually clarify that SWTOR has both fee based subscription based gaming and free to play. Naturally, there are more F2P players than there are players paying the monthly fee.