What they´ll do may be one thing, what they should do another.
I don´t believe the Otus will have any impact on Canon´s plans. It is more than twice the 1.2L price, so even though it is better, it is big, expensive and manual focus, so I don´t believe they lost their sleep over that one.
But with the Sigma Art, it is different. Up until the Sigma came about, the offerings from Canon was OK, compared to the competition. I still find the 1.2L excellent for its use. But with the very competitively priced Sigma Art, Canon, like Nikon, is left in the dust and in my view, they must do something.
I think the f1.2 feature on the 50mm and 85mm is a magnet to many photographers, even though it matters close to nothing in practical terms, compared to f1.4. So a new red ringed 50mm (and 85mm) at f1.2, with IS, would tempt a lot of photographers, provided the IQ competes with the Otus and the Sigma.