Stance: Selfcest/Mirrorshipping is Cuashipping (usually)
These kind of ships draw a lot of controversy over whether or not they are proship or incest adjacent. I see this stance as entirely reasonable. Mirrorshipping is a grey area that can cause discomfort. While I don't doubt that some people are using mirrorshipping as a vehicle for proship/incest fantasies, I think that these cases are negligible compared to the selfcest scene at large. Mirror ships are often composed of and treated as relationships between Consenting Unrelated Adults. Thus, a valid cuaship.
"But wait!" I hear you say. "Self is a relationship! That makes you related!" Sure, you could argue that. That's partly true. However, what separates selfcest from incest is the harm. Incest is always harmful even if between "consenting adults" because it always contains some kind of abuse or unsafe power dynamic. It does not occur in any way that is functional or healthy. It ruins lives and weakens the health of your family. In fiction, glorifying, romanticizing, and normalizing these relationships has psychological consequences.
But mirrorshipping isn't like incest. Not only is it not like a relationship between family members (i.e. one that will have consequences and cause damage), but it's a complete fantasy. You cannot ever clone yourself and get romantical with the clone. Mirrorshipping also takes on many different forms, where it's arguable that in many cases the two "same people" are actually very different people.
In the end, the way a mirrorship is handled is what draws the line between proship and cuaship.