In the staff commentary of Mahou Shoujo Madoka★Magica
Blu-ray vol.6, Urobuchi Gen
has announced that he is working on the next work of madoka.
Urobuchi: It's been quite short since I began to work in the anime industry, but I was fortunate that the producers of Madoka let me do in my own way. In order to show my gratitude to the staff, I'm struggling to work out ideas of the next "thing". I think I can announce it someday.
Yuki Aoi: Second season? Second season?
Urobuchi: I'm twisting my brain now.
Yuki Aoi: There could be a parallel world or a different ending?
Urobuchi: Possible. We won't let Madoka go.
Source: Madoka Blu-ray vol.6