This is actually not true, Ten were bidding for it back in 2011.
The fact that the show isn't in Nines up-fronts yet means nothing. They don't have the rights for it next year so why would they be advertising the fact that its back? I say give it time and we should hopefully know the "winning bidder" of the rights by the end of the year.
Another thing we need to think of is I can't see Sonia travelling all around with baby in toe to host the series, if she does it will probably be only the eviction show. I can't think of any other Nine stable celebs that could host it either.
I really think (and hope) that the next round of negotiations for the contract have Endemol fuming at how Nine have treated the series and this ends up in Tens favor.
If the show goes to Ten, then Sonia won't be hosting, as she is contracted exclusively to Nine. Ten would hire their own host.
If it stays on Nine, and Sonia has to take leave because of Heffley baby, then I'm not sure what Nine will do. Hmmm.....Maybe Tracy Grimshaw, Eddie McGuire or Karl Sefanovic filling in.