I...So what sparked the change for 'Ki' training to be explicit? When I talk about Ki I dont mean teaching it through Shugyo or Zanshin or other principles. I mean Ki as in Ki tests, following your Ki, extending your mind... etc.
Ki training probably became explicit because aikido moved westward. Within the Japanese culture the understanding of ki is implicit. In the west there is no tradition of ki, so an instructor had to become explicit so the student can comprehend. Koichi Tohei remarked that American students always asked questions. He would take a non-traditional approach to ki training and develop a curriculum that would parallel the aikido training.
When he started the Ki Society one would gain rank in both ki development and aikido. A student would need a certain ki rank before they became eligible to test for an aikido rank. From what I've seen of traditional training, the feeling is that there is no need to teach ki development, since it should grow naturally as one practices.