Info re. the expansions, from a Witcher 3 developer:
"The expansion packs will be whole new storylines with all the elements you've got in the main story (like cutscenes, new characters, new items, new Gwent cards) and many, many more.
They will be quite long.
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, because 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."
http://www.gamereactor.eu/news/329274/Witcher+3+expansions+"almost+size+of+Witcher+2"/
That's a lot of content. I'll be happy to pay. I haven't downloaded any of the free DLC so far. I've got to figure out how to do that, one of these days. There's so much else to do, though.
About that last bit ("very emotional stories"), I've been surprised at how good some of the storytelling has been in Witcher 3. I've actually teared up a couple of times. In Witcher 2, by contrast, I never felt emotionally engaged in anything that happened, throughout the course of the whole game. The writing and execution is a lot better this time around. There's a lot more humor, too.
p.s. I'm hearing the first one is set for October and the second in Q1 2016.