I hate when I try to empty the trash and I don«t got the privileges to empty it.
There could be a keyboard combo so when you try to empty the trash you would be prompted with root password if you don«t have the privileges to empty something.
Holding option down used to delete locked files. I think your idea is great. Shift-Command-Option-Delete to empty the trash removing locked files and prompting for admin password if and only if there are files that you don't have permission. Using a smart context sensitive feature like that would be great.