I would put the chances of Ebola-as-terroist-threat to be absolutely zero. There's simply no way to even handle the stuff outside of a level 5 biocontainment field without infecting yourself. It's way WAY out of Al-Qaida's league. It's even out of Iraq's league. Anyone who started playing with it would be dead before they even got to square one. If our enemies can't do it with anthrax or smallpox, there's no way they can do it with Ebola.
The only even slightly possible scenario I could think of would be another Al-Qaida suicide nutcase going to Africa, intentionally infecting himself, and then hopping on the next flight to the US. And even that wouldn't work, because he'd show symptoms long before the plane ever made it here, and the plane would simply be quarantined. He wouldn't even end up infecting more than a couple of people on the plane, either, unless he started running up and down the aisles licking people, which is a great way to get yourself tied up and/or killed in and of itself these days.
I'm not even totally convinced that Ebola Reston is truly airborne. I think it's quite possible they simply missed some physical contact between parties somewhere in their investigation.
Ah there's the rub,if you have people prepared to die!
It would have a nasty way of coming back to you though.