The good old Dark Castle is getting sad and old with the introduction of new fancy house. It has room for 100 settlers on a footprint 3,5 times that of a noble (max 70), witch tower (100) or frozen mansion (140).
On a crowded island there is no room for such a poor building anymore, and soon people will find it hard to give them away.
The population of the Dark Castle should be increased to at least 300, preferably 400 to make it a desirable building for longtime players again.
And for the record, I sold all of mine several months ago