I love the Goto Anything menu, I use it religiously. I also use the more specific Goto menus, like the line, or symbol ones.
I find myself often hitting the keyboard command for another Goto action while using the Goto Anything menu. I think this addition would be useful and easy to implement.
Here's an example of how it might work:
Hit Command-P, start typing the name of the file and narrow it down, highlighting the one you're after.
Now press Command-R, you are now searching through symbols in the highlighted file. The string in the text field for the Goto Anything menu shows an "@" appended. You can backspace to return to the previous state.
Customer support service by UserEcho