By funny coincidence, another big MMO happening just went down. The Secret World recently relaunched as Secret World Legends, going from Pay-once to free-to-play, making minimal changes to the funding model, and using the opportunity of the relaunch to completely revamp the game - everything from skill changes, to an entirely new combat and movement system, to revamping every single one of the hundreds of quests in the game with everything from minor tweaks, to entirely new animated cutscenes and dialog - using data pulled from years of player experience surveys, patch reactions, in-game data collection, and so on.
Now, this wouldn't be weird for a small-time, not particularly successful MMO, but as I'm sure I've said before - The Secret World was quietly one of the most successful MMOs in recent memory. It's profits alone were enough to not only keep the game running, but also kept the entire Funcom studio in the black, and fund the development of multiple titles, including at least one large-scale AAA title. They took their entire, hugely successful product, changed almost every aspect of it(and at the very least, revised and revamped what they didn't change), and re-released it without the payment for entry, or the paid content.