Assuming that McCain really digs in on this and does give in and support the bill, the Webb bill will be a highly effective issue with which to bludgeon McCain all the way through November. McCain's big strength is his status as a veteran and supposed defender of other veterans. The GI Bill is a way of demolishing what is supposed to be his strongest point, while doing so in a way that does not impugn McCain's personal service to his country during the Vietnam War.
This is going to be very useful. It's a far cry from what Jim Webb wanted to happen when he introduced this bill, but if it's handy then let's use it until the bill gets passed.
The gravy on top would be selecting Jim Webb as a running mate, keeping McCain's failure to support the troops right up there in the headlines all the way through election day. Jim Webb can tear into John McCain for failing to support these combat veterans in a way that Barack Obama would have difficulty carrying off on his own. It would be a game plan for an attack against McCain that need not disintegrate into the kind of ugly politics that Obama despises. This is something substantive which needs to be publicly debated.
Obama/Webb 2008 would be the real dream ticket.