This is all I could find:viewtopic.php?f=9&t=11344
It would seem that the 4x4x4 morphix puzzle, dubbed the megamorphix was started many years ago, not sure if it was completed or not.
As far as i know, 6x6x6 morphix's and up have not been made.
6 should be easy enough, and I actually I think
a 7x7x7 morphix could be made without pillowing
all flat surfaces with the expected evenness of the slices. Not sure yet though.
Then again, the bigger the morphix, the larger the four corners, which are really only necessary for the shape and really waste alot of material and greatly add to the bulk of the puzzle. A 7x7x7 morphix would have to be huge....