We have discussed bits of this here and there but hopefully now we can have a consistent decision:
We accumulate hundreds of open bugs and enhancement requests under the Extensions product, and many of those fall under extensions that are explicitly archived or no longer maintained.
I believe it is OK and even healthy to take all the open reports in an abandoned extension and assign WONTFIX (if the project is explicitly abandoned but their maintainers) or Lowest priority in case of doubt.
This way we can keep our focus on the areas that really need cleaning and have active contributors directly benefiting from our triaging work.