At the very least, shouldn't MoP get polarized filters for their screens, so nosy photogs can't (so easily) snap pictures of briefing documents, as happened to Kissinger and others?
iPads are no more or less secure than paper, which I would use as the relevant baseline. iPads are also lockable, so they're not immediately accessible if someone leaves them lying around -- try that with a document printed on dead trees.
You can certainly enhance security beyond that -- have iPads that are remotely wipeable, or even automatically scrub documents if they connect to an unauthorized network. Keep any sensitive documents on a server on a secure network, with no local storage or caching, so a stolen iPad doesn't have any information of great value on it.