Speaking of which, a Pedigree Collapse or Endogamy sticker might actually be useful--to alert any descendants of that fact. Whether it was incestuous or not is largely irrelevant to genealogists, but pedigree collapse is relevant. For one thing, it can mess with relationship estimates, making them seem closer than reality.
I was thinking sticker (vice category) because the fact that an individual shows evidence of collapse is important, but the grouping of that individual with others is not very helpful. Such a sticker might have variables for broad classes of reasons, such as endogamy found in royal families, tightly-knit communities, etc. If the best way to implement a sticker is to have it send to a Category, then so be it.
If enough people think it's useful, I could post a separate G2G question/suggestion on it.