I've thought through features like the blog and making it possible to add keywords and description from within different features. I have a plan for that.
Pages like Register and Login are a different animal. I could add site settings for those, but I'm interested to know what is considered best practice for those pages in terms of giving them key words or description. They are not content pages, so it seems to me this should be minimal data there just indicating the main keywords and description for the site (as it does now) or even less info, maybe just something indicating the site name and the purpose of the page.
Before I put my time into making those pages customizable I want to hear the business rationale of why that should be customizable and an example story of how you would use it and why.