That's funny, I was just pondering the same thing. I am booked on an A330 at the end of August 2012 in first from IAD-FRA.
Would be a VERY lucky break if it gets changed to a 748 (but I doubt it).
Is there any talk of the routes they are planning? I am also flying FRA-JNB on the A380, but I am sure they won't substitute the 748 from the A380...right?