Thought long and hard, still not sure to be honest, but here goes.
Basically. BW is/are clues (a la Next Gen) left by someone for CE's Doctor. Could it be as simple as telling him to "reverse the flow"?
But who's leaving the clues?
30: DT's Doctor to his former self.
40: The Time Lords. If the Daleks survived the Time War in some other dimension, surely the Masters of Time would have been able to? Bad Wolf is/are simply their clues to their last surviving member to save them...
20: This is actually the start of the Time War. I explained this theory of mine weeks ago, involving highly improbable appearances by Paul McGann's Doctor. Hence the clues are from PMcG's Doctor for his
future self.
10: Something involving "The Watcher". Someone in the pub I drink in thinks CE
is the Watcher...
Of course, as per RTD on the Bad Wolf website...
Quote:
“"Judging from the reactions I've had, a lot of people seem to think the Bad Wolf has already been revealed. Oh, it's the TV station. Oh, it's half a million Daleks. I've even got one friend claiming it's the Face of Boe! I must get better friends.
"I don't want to give anything away yet, but there is another revelation to come in Saturday's episode. We haven't discovered the true Bad Wolf yet."”