Just found this excellent video series on Morihiro Saito's traditional approach to aikido.
Here, he gives some explanations about the "fluid" number of aikido techniques, and how he could come up with almost infinite variations on one technique:
Takemusu-aiki-curriculum-(1994-09).mp4
Here, he discusses application. Oyo-waza are techniques from the kata applied to a particular situation (e.g. sparring), while henka-waza is the term for when you try a technique, it doesn't work and then you switch to another one:
Oyowaza-and-henkawaza-(1992-09).mp4
I've often wondered why I had never been taught oyo-waza. No teacher says "ok now we're doing applications" and there's almost no trace of them in reference books. From Saito's explanation above, I get that teaching oyo-waza would be moot: I can't teach you adaptability by teaching the 7th oyo-waza version of X technique which is only appropriate when uke has his weight on his nearest foot. Instead I teach the basic form as a drill, and you're expected to make it work.
This clarifies a bit the training model of aikido. That said, I still think that the sparring/randori format could be improved (a lot) to facilitate learning oyo-waza and henka-waza. It's a big part of what makes competitive styles like BJJ, judo and wrestling effective, along with more extensive technical and tactical study.
Bruce Bookman has some great ideas on oyo-waza and henka-waza. See how he has systematized follow ups to classical aikido technique:
First, here's the classical shiho nage:
Now, here's Bookman's shiho nage to sankyo:
Here's a sankyo follow up when uke rolls out of it:
Although I'm more interested in the body skills developed by aikido because the techniques were poorly thought up, I think he's onto something with his work.