if you want the 6.2, wait. there is no proof it is coming though.
the 6.2 is very likely to come to the Expedition. But for now Ford is playing things close and not telling us what is forthcoming. Look to the F-150. if the 6.2 goes mainstream in there, the Expy is 99% likely to get it as well.
sounds like you are going to have to wait for a 2012 model though really