I must stress this: RUMOR, RUMOR, RUMOR! NOT CONFIRMED! MOST PROBABLY COMPLETELY MADE UP, PROBABLY WON'T EVEN HAPPEN...!!!
Right... on to what I found. Brace yourselves.
Following are speculations for Season 4:
40X. Voyage of the Damned
Christmas Special by Russell T Davies
The Titanic crashes into the TARDIS just as it is dematerialising. The Doctor finds that time is being manipulated by some spikey aliens called Porgs and he gets the help of a young waitress aboard the Titanic. It is about to leave on its maiden voyage so the adventure will probably continue until the ship strikes the iceberg. Hmm. Does this mean that the iceberg was really a space ship or that the invasion of these aliens actually caused the ship to crash?
401. Fires of Vulcan II (Suggested Title)
by Russell T Davies
Donna Noble encounters an alien emergency in London and there's only one person she knows of that can help her. But what has ancient Rome got to do with anything? A quick trip to Pompei when Mount Vesuvius is about to explode. Can they save all the people?
Donna and The Doctor visit Agatha Christie, played by Fenella Woolgar, and together they investigate a strange murder. The Doctor begins having flashbacks to the Time War. Something is starting to affect his past.
403. Planet of the Ood (Title in a news report)
A trip to the far future. The Doctor remembers his eighth incarnation and knows that a storm is coming. Something he'd forgotten. Something to do with Davros. Something buried in the bowels of the Ship, Chesterfield. Donna has to deal with some Ood.
404. A Deadly Past (Suggested Title)
405. Axonite (Part 2) (Suggested Title)
By Terrance Dicks
Something has taken control of the TARDIS. Something that has been trapped in a timeloop in geostationery orbit above Britain for 30 years.
The Axons are back!
406. Sapphire Avenged (Suggested Title)
Joanna Lumley takes on the role of the Master, while John Simms reprises his role as the Master's spirit. The Doctor and Donna track the Master down in the year 100 trillion.
407. The Icy Nemesis (Suggested Title)
A strange signal is being received from Mars and a retired Brigadier is asked to help decipher it. He calls on the Doctor for the first official meeting of Earth and the Ice Warriors. But they can't find the Doctor. But they can find Martha Jones.
408. Eternal Triangle (Suggested Title)
409. Destruction of the Daleks (Suggested Title)
Time continues to change. The rupture caused by the Axons is starting to pull the Doctor back into the Time War. He knows he destroyed Davros but now he's back (Played by Ben Kingsley) And what do the Eternals have to do with things?
More flashback scenes of the 8th Doctor during the timewar, including the moment when Davros kills him.
Martha and Donna get on really well in this story!
410. Time War Part 1 (Suggested Titles)
411. Time War Part 2
412. Time War Part 3
413. Time War Part 4
The Time War has changed. The outcome is different. The Daleks have won. The Doctor needs to go back and change time again. Watch the death of his fellow Time Lords again. Watch Gallifrey burn again. But he finds a way to change everything. The Time Lords can live again but it may cost the Doctor his 10th life.
This would also be story number 200 and worth a celebration in itself.AND there is a rumor floating about about the return of ROSE. But, as I have said for everything else in this post. IT IS JUST A RUMOR!