Its definately possible.... someone did Cape to Cairo in 18 days a few years back, but who really wants to rush like that ?!
Things change a lot in Sudananese bureaucracy, but it was and possibly still is, pretty easy to get a visa in Egypt from Aswan (best) or Cairo. May take a few days but its worth the wait Id say.
Enjoy Wadi Halfa, its a great place- neat tree lined streets, a cool breeze in the afternoon, great restaurants and the night life...! hee hee hee
"If we don't find something good at least we will find something new." Voltaire