What will happen when a D400 comes

Yes, this will be interesting when you have a high MP FF sensor combined with an EVF.  Then, you can actually see a DX crop as full screen EVF in the viewfinder.  But, it will still cost as much as an FF camera (because it is a FF camera) so while it may be interesting for those who can afford expensive FF cameras (e.g. $3k) and occasionally want to shoot in DX crop, it won't fill the lower price levels that DX cameras occupy.

--
John
Gallery: http://jfriend.smugmug.com