Some ideas about expansion of some of their products to include other girls:

The travel adventures:
Kirsten's travel Adventure-in a stagecoach, maybe on the Oregon Trail or to visit Marta's family somewhere
Felicity's travel adventure(in a carriage), maybe to Boston or Richmond or something
Josefina's Wagon Train adventure
Still trying to think of one for Addy

Friedship Fun books for all the other girls

Also, maybe an Amelia doll to go with the successful Amelia's Notebooks series

LiveStrong bracelets for the dolls-very popular, either LiveStrong or American girl

And, there has to be a book where Agnes and Agatha meet Nellie and her sisters!

For Halloween-a Dorothy outfit, either for AGOT or Molly!

Kit-Shirley Temple outfit