Changing the way we index posts and topics for search is always tricky. My hesitation to major changes stem from the fact that we don’t have a good way of knowing the full impact of the changes whenever we roll stuff out. We may be making search better for a certain case and making search worst for other cases.
Maybe the first small step we can take here is to support search with different indexing strategies? For example, we make it possible to allow site admins to specify that category and tag names for a post should be part of the A weight instead of being part of the B and C weights respectively. Then we can at least try that out to see how it feels before making a decision on whether we should roll out the new indexing strategy more widely.