Currently, magic words on global user pages come from the remote wiki (meta). It'd be nice if they were rendered from the local userpage.
One use-case for this would be {{#babel:{{CONTENTLANG}}-0}}. Another might be to show certain messages on e.g. all Tamil projects, but not on others.
GlobalUserPages are 100% parsed remotely, meaning that everything is parsed in the context of meta. The only exception to this is that the page will be parsed in the language of the user viewing the page, so you can use {{int:lang}} hacks on meta to get the interface language of the user viewing the page.