I think it's important to distinguish between what the intent of a law is, versus how the law is enforced. In other words, you never really know the effects of a bill until sometime after it becomes law (typically a year).
With that in mind, email marketers who already follow best-practices for opt-ins (for mid-tier providers, MC is particularly good about enforcing these best practices) should be fine under CASL.
Best practices for opt-ins (for example, not using "old" lists", explaining how the recipient opted-in in the first place) are intrinsically good, resulting lower spam flags and complaints, higher engagement, and (the point of email marketing) higher conversions.