It is true that in the Iwama weapons system the bokken is generally considered to be a striking weapon. Do you have a reason to believe that at some point, the founder held a different view (say, that the bokken is just an approximation if a shinken) and the change of shape reflects a change in the attitude?
The idea that aikiken training as conceived by Ueshiba ever
used the bokken as a striking implement and not a sword is really the more outlandish claim. Ueshiba was a swordsman. His primary teacher was certainly a swordsman. An aikiken system that treats the bokken as a club or staff instead of a blade seems deprived and deranged to me.
There are two things that the blunt kissaki of the Iwama bokken shape brings to mind for me:
1) Much safer if you accidentally thrust into your partner's body while training.
2) The bokken they use in Kashima Shinto ryu these days has the same tip, though it is not curved. I assume they have been using that form of bokken for some time.