Spoiler tiny text, lots of spoilery stuff for Season 4:
The Rose thing is not a shocker. I would be shocked if we didn't see at least her/Martha/Sarah Jane/Jack at random points leading up to near the end of Series 4. I'm fairly certain it's been confirmed that all 4 will be in at least ONE episode, if not multiple, this year, as either part of the "Who Lite" episode (each year so far has had one, where the Doctor is barely in the episode, a break for the actor, last year's was "Blink", and the one with the LINDA folks are examples), where several of the Doctor's assistants will somehow band together. The other rumor I heard was that they would all be involved, including Rose, in the season finale, which should have something to do with Davros. Either way, can't wait for Jack and Sarah Jane
That said: I really adore this show, and I like Donna more than either Martha or Rose, I thought her character was absolutely fantastic in the Runaway Bride.
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