Julius James, I believe, does not have a future as a defender at this level. His ability to read the game seems severely limited, his positioning is very poor, and a couple of times he's literally been caught frozen in spot and giving up goals, with the Twellman header perhaps the worst of them all (although watching Mike McGee blow by him unchallenged was a close second.)
But, he is quite obviously a superb natural athlete. He has a tremendous vertical leap (over 30") and, having played centre back to this point is an excellent header of the ball. This has been reflected in the team targeting him on set pieces, and Carver moving him up at the end of one game (can't remember which) to play as an emergency striker.
It's not unprecedented. Jan Koller and Kevin Phillips both started as defenders and Mark Hughes (if I've got he right guy) actually played both. So has Kevin McKenna.
I say Carver takes advantage of what little youth dev time the guy has left (he's 24, so he's about four years away from a striker's peak) and grooms James to be the successor target man for Danny Dichio, filling a role every team could use for versatility's sake.