I think the senior shihan that Homma is referring to who changed his suburi and his kokyunage is Saito Morihiro. I didn't know that the reason for the change was the deterioration of his knees.
Yes, Saito Sensei was my first thought too. I have noticed changes in how Saito moved as he got older (his kamae was originally much more like the "standard" Aikikai one).
The really strange thing for me is the way so many people in the "Iwama Ryu" tradition, having swallowed the line that "this is EXACTLY how O-Sensei practised", copy Saito's posture even though their bodies are healthy...