what's really relevant is what kind of staff, and what kind of diplomatic rank (protocol office, media office, EC staff or personal selection, etc...) he gets, because that will in turn drive what kind of attention the job can garner, and what kind of influence it will have. In the long run, we're all dead. John Maynard Keynes
He won't want the EU job unless it comes with a shiny tiara and - more importantly - the chance to make even more money.
The downside is that if he gets the job, the UK Eurosceptics will feel vindicated in their EU loathing.
And that might not even be unfair, considering.