So lets discuss this...first of all castle does get some good LEGO loving every so often..I mean come on MMV was a dream! Now the joust set...not my thing but it was/is good too. Both marketed toward the AFOLs not so much the kids. You know...the exclusives.
Castle is an evergreen line, but...have you really been very happy with the castle sets...other than the figs and accessories? Really? I look at the sets and think..."oh joy more big wall pieces..." by the way...I loathe big wall pieces. They take up too much room, and they just aren't something I like/want to build with. It's a personal preference for my own building. Every line that comes out...more and more people say "it's so...juniorized." But we never know what is coming next...
Unfortunately, one can't compare castle with Star Wars. SW is the highest selling line...kids and adults want those ships. Yes, they will make huge sets for it and they will sell.
Would a big castle be nice? Well sure...but I almost think I would look at it as a parts pack instead of a castle. Why? Because I like building castles MY way and as bad as this is going to sound...no way LEGO will build them that way.
So sure...bring a big castle. One day I might build in bley...
But if you want to make me happy...give me one or both of the Frozen castles. Both are nice, big, and they would be epic full of amazing details.