Interesting theory:
a) What reason would Dawn have to go to Pallet Town? May went there because the next region took place in Kanto, but unless Dawn is doing contests in Kanto next, what reason would she be there?
b) A Pallet Town ep doesn't always mean a Misty appearance. The last AG episode was at Pallet Town, and Misty was not there. While she will probably be there this time due to the 270+ episode gap of when she last appeared, (it'll be nearly 300 eps by the time Sinnoh is done), do we know Dawn will be there as well?
From the way this gen is playing out, it's quite possible the writers never really intended to have the two meet.
Well now that you think about it,it is posibillity that Dawn could part off not going with Ash and Brock to Pallet,but than again taking into account that lure which was brought up(Dawn seened interest into her) its possible that writers perhaps are planning to have those two meet afterall.
Also what can possibly guarantee that Misty wont show up somewhere else instead of Pallet,with writers avoiding repetitive scenario second time around?Of course in Sinnoh probably not,
unless Misty comes in person at Sinnoh league(sure she didnt came for Hoenn,but given the long gap of absence who can say that this time around this wont happen?).
For all we know she could even return to cast for next region(this option has the least probabillity despite reasons for it and how great this would be).
Going by Sinnoh,and return of long ol time forgotten characters like Gary,Butch and Cassidy,Jessibelle almost everything is to expect.
Possible scenarios of Dawn and Misty having meeting:
-At Sinnoh league
-at Pallet Town with Dawn heading toward it with Ash.
-one of options was for filler arc(but given the new turn of events,it seems this isnt anymore optional).
-Dawn staying for next region,and Misty joining group finally meeting.
Of course some of above examples are not very likely,but i provided all options which would allow their meeting.
If they dont however this would be a shame because both Dawn and Misty are great characters,and their meetzing could made interesting encounter.May and Misty had pretty good chemistry forming nice friendship,and given the(of course both have matured but this was always present) Dawn being girly and Misty being hotheaded they could develop good relationship.