Here is some fan work of the elements of harmony and who fans believe the new barers are going to be.
For this element, as Applejack has the element of Honesty to begin with, most fans would get her to give it to Apple Bloom.
As Rarity is the element of Generosity, Sweetie Belle is the most common pony to be given this element. However, others include Rumble, Diamond Tiara, or some other foal out there.
The most common choice for this element is Scootaloo, because Rainbow Dash was the original barer, and Scootaloo idealises her.
With this one, there have been many creative thoughts and quite possibly more until season 4 comes out with all it's episodes. There has been Sunny Daze, Peachy Pie, Dinky Doo, Pipsqueak, Babs Seed, and some others as well.
Sometimes, Sweetie Belle is this element for her taking a little after Fluttershy. Others for this element include Pipsqueak, Peachy Pie, Cotten Cloudy and Babs Seed. A more recent one is an OC by the name of Heartsong.
This is the hardest one for most fans to find a pony to bare the element. So far there has been in fan work: Sweetie Belle, Dinky Doo, Ruby Pinch and Toosie Flute. More recently has been an OC named Fictionary made by MarzipanHomestar66.
Possible changes that fans might like to do
Since "Apple Family Reunion", Babs Seed mentioned 2 new friends in Mane Hatten. This gives fans the choice to change their fan fics up to include all the CMC into the elements of harmony, or to leave the fan fics as it is. It is best to wait for season 4 to roll around though.