1) for 3.6 (or later if not posible) :
We would like to be able to have a custom field type that allows us to select information (field) from user's profile.

NOTE : that would become more usefull when linked issue http://jira.atlassian.com/browse/JRA-1519 will be resolved.

2) for 4.0 (or later if not posible) :
calculate something... using several fields... or fields from issue and from user's profile....
ex : substring, concatenates, regexpr... or math depending on field type.

NOTE : that's probably not so important as i think we can make it with plug-ins. but the best is to be able to do it the easyest way...