No Brock!? No 3rd Wheel?! No Dawn!?!
BTW, judging from what Ash said at the end of Hoenn, each adventure takes only a "couple of months" so let's put it at 4. This means that Ash is 11, Brock is 16, and Dawn is 10.
Realistically though, would you think having Dawn tag along with Ash and the new female companion benefit Pearlshipping? If Brock joins them aswell, will this change your answer?
If one thing in BW is certain, it's that Ash has a new female companion. I think it would be really cool to have Dawn and Ash travel to Isshu, meet the new girl, and find Brock a few episodes later meeting up with them. That way, it will be like Hoenn, a 4-person gang!
And this is where it gets interesting. Dawn will pursue contests, while the new girl wants to pursue Gym battles, like Ash. This forms a love triangle between Ash and the two girls, and Dawn gets jealous because the new girl likes Gym battles, just like Ash.