Some tasks that have been mentioned elsewhere that would be nice to have in the debugger:

• Make breakpoints at labels
• Handle restart opcodes - though I'm not even sure what these opcodes are at this point (--coke)
• Attach to a running program
• Prior art:  http://xdebug.org/docs-dbgp.php
• clone the interpreter to allow people to play into the debugger and then continue the normal execution of the program