Currently, there are only two institutions with the power to regulate the steam workshop, them being Valve and Paradox (or Colossal Order).
Valve has stated numerous times that they cannot and will not conduct any policing of the Steam Workshop, as it would cost too many resources for very little benefit, and in the end they love to hide behind the "laissez faire" approach, where the community is supposed to differ good mods from bad by rating, subscribing, commenting, whatever.
Paradox (or Colossal Order, depending under whom Cities Skylines is published) who in theory should have the biggest interest in actually cleaning the Workshop up, considering their heavy focus on game moddability and the subsequent advertising of this fact. That being said, it's unlikely that Paradox Interactive (the publisher) has the resources or knowledge to distinguish between good and bad mods, and expecting Colossal Order to do such a menial task would be a strain of their resources, and in the end it would only result in less content for us, whether in terms of patches, DLC, etc.
For those reasons, any expectations of the developers/publisher to actively moderate the workshop are folly and unlikely to happen in the near future, if ever.
However.
To my knowledge (and correct me if I am wrong), it is possible to give 3rd party persons the authority (as in administrative authority) to flag (if not outright remove) Steam Workshop content. In an ideal scenario, these would be various volunteers that have previously contributed towards Cities Skylines (e.g. experienced and popular modders, asset builders, community helpers, whatevs.) who would contribute their free time in cleaning up the workshop, removing copied or duplicated content, alternatively removing content that is in the end not that good without any expectations of payment, similar to the moderator system on the pdox forums (although I am speaking out of my ass here, as I have no idea if the forum mods are employees of pdox or are being reimbursed in any way, shape or form for their work).