WoW took a long time to get where it got - they've plateaued. They can keep adding content but it will always follow the same formula. I loved WoW, but I've hit end-game too many times. I still check back in now and then.
SW has a long way to go. But they have a structure that is absolutely fantastic, much like WoW did. And here the story is really important. Because of the interactive quest pick up/drop off - you know what you're doing in regards to class and planetary progression. You are less likely to skip a quest conversation when you get to flirt with your quest giver.
I am excited to see content patches from SW in the future. Not that I don't have plenty to do now - but I am really interested to see where the game goes from here on out.
As far as taking over WoW? For most of us gamers nothing can replace our time spent getting killed by and killing Rogues near TM, hating our GM's, collecting pets/mounts, jumping off tall buildings, or leaving critter corpses laid out spelling KEK in big empty fields for mounted explorers.
SW is a different game. And it will go in a different direction. I plan on staying around for a while to see where it goes.