It does hint at one of the problems that this current form of Labour would have in power though. When you're that close to the unions, you really have no choice but to say yes when they ask for improved terms for members, or you face accusations of hypocrisy.
But what happens if the unions start asking for improvements in terms that are completely OTT? Its not their role to worry about Government finances, its their role to campaign for their members, so Labour can hardly hope that they'll just be reasonable. In a weird way the unions are more of a threat to Labour than to the Tories. With the Tories, its a given that they'll be butting heads with the unions, no-one expects otherwise. But widespread action by the unions against the decisions of a Corbyn led Government? That could have all sorts of strange consequences.