As much as we would all like to give the impression that the cryptocurrency market can be predicted with certainty using numerous theories, such as the 4-year cycle theory, which is meant to anticipate both bull and bear markets. While all of this has historically been demonstrated a few times, there is no denying that the landscape of the entire cryptocurrency market has fundamentally shifted as a result of this recent mainstream adoption.
By my understanding of mainstream adoption, I wouldn't say cryptocurrency have achieved that; we are still far from it even though we have made remarkable progress in terms of awareness.
I will be comfortable to say cryptocurrency have achieved mainstream adoption when it becomes legal tender in several jurisdictions and readily accepted in various merchants and businesses across the world. This will come when there are innovations that make cryptocurrency attractive and a better alternative to conventional way of doing business.