What does it mean to say that consciousness (really subjective experience) is an illusion? An illusion implies the ability to have illusions. So it doesn't make sense to me to say that consciousness (subjective experience) is an illusion. The experiencing of the illusion is subjective experience. Not quite Descartes, but close.
This isn't saying that I am proving my existence because I experience myself thinking. But it is saying the having of an illusion by definition is a phenomenon that requires consciousness.
It may also be that the experience of thinking (in Descartes' version) similarly (again by definition) establishes the existence of the thinker. That is if one grants that one experiences oneself thinking then by definition whatever is experiencing the thinking exists.