While some of the logistics will need to be worked out, I think that this is an excellent idea and I applaud McCain for suggesting it. If done properly, it could provide a more effective way for the legislature, specifically the minority party, to interact with the Executive Office. It would also put some pressure on the President to be well-versed enough in the issues to take on adversarial questions. That would be a pretty big benefit.
He has also pledged to hold weekly press conferences, unlike Bush, who has tended to have them only once a month.
McCain has started to lay out his vision of how he would run the Executive Office and I like what I am hearing.