Feature summary (what you would like to be able to do and where):
Some way to affect a local user page's display title formatting should be offered.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Currently, if a global user page User:Alice formats its display title using {{DISPLAYTITLE|User:alice}}, that magic word will never affect any local user page User:Alice.

Benefits (why should this be implemented?):
Implementing this allows display title formatting between a global user page with non-default formatting and its local user pages to become more consistent.