Add a config option to allow the login / create account link to be split into separate login and create account links. (Besides Google and Bing, Wikipedia/MediaWiki is the only big site I see that actually doesn't provide separate login and create account links).
This is partially made because there are skins where separate login and createaccount links are made, not giving them proper login and createaccount links in the personal_urls means partial reimplementation of personal_urls code in the skin (or worse, no support for features like $wgSecureLogin in these skins when they don't keep up with core).