A Golden Sun remake or sequel would need to look unique and special to stand out from the pack today. On the GBA, the game was the graphical showcase of the machine with its 3D tricks and particle effects, and stunning music coming out of those tiny speakers. Golden Sun first got on the radar for it's production values on those stunning summons, and Titan Blade unleashes. The rest of the game (dungeons, battles, djinn, story) helped put the title on the map and cross that million world-wide.
I think games like Octopath Traveler garnered attention for it's unique use of the Unreal 4 engine for a classic sprite game.
With Golden Sun, they can go in several directions that aren't triple A. Maybe they can work with, say, Arc System Works and have that Dragon Ball fighterz/ Granblue Fantasy Versus/Guilty Gear artstyle tailored for a traditional Golden Sun RPG.
Grandblue Versus trailer:
Or they can try and push for detailed HD sprites and make a modern Golden Sun/SNES game using today's advanced tech and art knowledge to make a graphically pleasing 2D game for the modern era.
Or they can go for Zelda like cel-shading, but that seems expensive to nail down, and I don't know if Camelot's artists or whoever they outsource to would be able to help Golden Sun stand out in that style without a Zelda budget or resources. Dark Dawn didn't really catch anyone's attention with it's reveal trailer beyond us hardcore fans who freaked out over Reggie saying the name "Golden Sun DS."
Golden Sun DS trailer:
And here's a trailer for Golden Sun "Dark Dawn":
And finally here's footage of the original Golden Sun on GBA:
I think I saw that footage at a KB toys store a loooong time ago. I also remember this little video that played on Golden Sun's website with fondness:
I don't know how Golden Sun should come back, but I hope it does and is still able to engross us in its fantasy setting, lore, and magic. My hope is that our momentum from last year could yet pay-off in the next year or two from now and we'll see our Golden Sun Re-Risen, be it in Smash, a remake, or a new game.