Richard Harnack wrote:
Ki is the central character of Ai Ki Do, it cannot be excluded. Neither is it preeminent.
True, but the term "aiki" in and of itself had been in use for hundreds of years prior to the "coining" of the term "aikido." Teachers in the Daito-ryu Jujutsu world (like Sokaku Takeda sensei), for example, use the term "aiki" very frequently and not as the usual aikido definition of "blending with ki" kind of thing.
I recently read a book called "The Invisible Power" ("Toumei no Chikara") which was written in Japanese by a student of Sagawa sensei. Sagawa sensei had studied with Takeda sensei for a long time and had "found" the power of "aiki." There are many interesting anecdotes of Sagawa sensei's throwing people across the room (in the opposite direction of the attack) with just lightest touch. This sort of thing (of making uke's strength disappear with any sort of contact) was what he called "aiki."
Personally, I've met plenty of people who do not use the concept of "ki" within their training and/or teaching who have, in my mind, wonderful aikido...