One killer feature which is missing atm is the ability to do something similar to Pry where you can change the values of variables on the fly during debugging. Right now the plugin doesn't allow one to do this however I believe its possible to do with the standalone tool.

On a related note it is also possible to execute functions in Pry whilst debugging by dropping into an IRB like prompt whilst debugging the code. Having something similar to this ability for this plugin would cover a lot of missing functionality as well.