>> "if he travelled via Shannon as part of his efforts to get to Cuba and was arrested under the provisional arrest warrant pending an extradition process by the American authorities in the Irish courts, he could apply for asylum while being held in prison here." An interesting prospect but incredibly unlikely.
Non extradition due to death penalty might work anywhere in Europe. It might not if US says it won't execute Snowden (if they lie, then no one will ever be extradited on that basis again, as that would be illegal from then on).
For the sake of background: people bring up the prospect of the death penalty for espionage often in these cases, but it's not something the US has actually invoked since WWII, even in very clear-cut situations where money changed hands or people died as a result.
For example: http://en.wikipedia.org/wiki/Noshir_Gowadia http://en.wikipedia.org/wiki/Robert_Hanssen http://en.wikipedia.org/wiki/Walter_Kendall_Myers http://en.wikipedia.org/wiki/Harold_James_Nicholson