Stating that all future content and expansions will be free even outside of early access is a powerful idea. I'm not sure how it'll pan out for them financially, but as long as the core game is good and runs well I think that the incredible wall of paid content in the Sims and that immediate feeling of "I'm not getting the whole thing" when considering only buying the base game is definitely something that's basically stopped me from moving on from Sims 3.
Why go to 4 if I have a content robust game already, and getting a similar amount of content there would cost a small fortune? If a well playing competitor arrives with one base game price and a promise that future content comes free, I think that could be a real foot in the door for this genre.