I loved Golden Sun, but I don't want there to be a sequel. It was fine as it was, and there's something sort of cool about there only being the two games. You wouldn't want there to be too many games until is sucks right? And even one title (esspecially on DS with Touch screen Gimmicks) could ruin it. I don't want a Golden Sun Sequel for the sake of keeping it great.
I don't believe that they would make a game that doesn't have the same level of completion of the others. Here is a list of games they have developed including another RPG franchise Shining Soul.
* Shining in the Darkness — 1991 (Mega Drive/Genesis)
* Shining Force: The Legacy of Great Intention — 1992 (Mega Drive/Genesis)
* Shining Force Gaiden — 1992 (Sega Game Gear)
* Shining Force Gaiden II: Sword of Hayja — 1993 (Sega Game Gear)
* Shining Force II: Ancient Sealing — 1993 (Mega Drive/Genesis)
* Shining Force CD — 1994 (Sega CD)
* Shining Force Gaiden: Final Conflict — 1995 (Sega Game Gear)
* Shining Wisdom — 1995 (Sega Saturn)
* Beyond the Beyond — 1995 (PlayStation)
* Shining the Holy Ark — 1996 (Sega Saturn)
* Hot Shots Golf — 1997 (PlayStation)
* Shining Force III — 1997 (Sega Saturn)
* Shining Force III Scenario 2 — 1998 (Sega Saturn)
* Shining Force III Scenario 3 — 1998 (Sega Saturn)
* Shining Force III Premium Disc — 1998 (Sega Saturn)
* Mario Golf — 1999 (Nintendo 64, Game Boy Color)
* Mario Tennis — 2000 (Nintendo 64, Game Boy Color)
* Golden Sun — 2001 (Game Boy Advance)
* Mobile Golf - 2001 (Game Boy Color)
* Golden Sun: The Lost Age — 2002 (Game Boy Advance)
* Mario Golf: Toadstool Tour — 2003 (Nintendo GameCube)
* Mario Golf: Advance Tour — 2004 (Game Boy Advance)
* Mario Power Tennis — 2004 (Nintendo GameCube)
* Mario Tennis: Power Tour — 2005 (Game Boy Advance)
* We Love Golf! — 2007 (Nintendo Wii)
I pulled this list from wikipedia. I believe that I can safetly say that Golden Sun would be in good hands as they have proved their worth as RPG developers.