Re: Why no tsuba?
I don't imagine that I should worry that future generations, wondering what Aikido people in the early 21st century thought about tsubas, will read very far into this thread.
But it worries me that beginners might think of a tsuba on a bokken as a real piece of protective equipment.
The two times I hand my hands whacked so hard that I had throbbing aches that lasted for months, I had a tsuba on my bokken. It did not stand in the way of my partner's bokken, since the angle and maai were both incorrect for the form we were practicing, and we were going at it with more intensity than we should have.
(The only time I actually broke a finger, I was putting on my hakama, but that's a story for another thread.)
I really think tsubas are just for practicing particular techniques that use them. They are for things that should happen, not for things that should NOT happen.