Design the spire? Why not use the design of the spire that was there?
I get the feeling that the rebuilt Notre Dame is going resemble the job that was done to Soldier Field.
One thing about the spire that was there ... it was built in 1855, not in the 12th century. It might be nice to look at old paintings, diagrams, etc., and build a spire that looked like it looked before 1855.