There has been a lot of speculation about what the series following Gundam Seed Destiny should be. Personally I would like to see a third GS Series but this time from the POV of someone from Orb. The first series started out with Earth Alliance as the main faction (but shifted focus later). GSD started out on the Zaft Side (and again shifted the focus). I think (similar to GSD) we should see the Orb side this time with the protagonist being someone that Shinn wronged (boy isn't that a long list) during GSD. Maybe also a female protagonist this time.
A final movie would also be nice to close out the GS universe (similar to Char's Counter Attack). Final fate of Kira, Athrun, etc.