If any game developers want to see how to do additional content and DLC right, they need only look at CD Projekt Red, which has released swathes of free and paid for content for its recent release of The Witcher 3: Wild Hunt. However apparently we've seen nothing yet, as the next big expansion for the game is going to give players so much more to do, it will be like tacking on The Witcher 2 to the game.
"The first expansion will be around 10 hours and the second expansion will be around 20 hours… and I think it’s possible that they will be bigger," said developer Konrad Tomaszkiewicz in a chat with Game Reactor.
"It’s always like this (that when we plan some time or hours, it’s twice or something like this), but I’m not promising anything right now. And even now, if you sum up this 10 to 20 hours and you compare it to The Witcher 2, it’s almost the size of The Witcher 2. And it will be cool, it will be new stories, it will be very emotional stories and I think that people will be happy."
Of course with this much content, it means it's going to take some time to put it all together, which is why the first part of the expansion: Heart of Stone, isn't set for release until the this year. Part 2 isn't expected until some time in 2016 - so there's plenty of time to finish all of the other subquests you've been ignoring.