I can imagine Isaac's CGI reveal looking like something out of a Avatar: The Last Airbender (a show I think has a Golden Sun feel to it) scene:
https://www.youtube.com/watch?v=23x00x4WcHw
If Sakurai needs inspiration to envision Isaac amongst the Smash roster, he should check out Toph from Avatar: The Last Airbender. She's a earth bender, as Isaac is an earth Adept and both can manipulate earth with the palm of their hands. Isaac also has djinn to draw more various elemental power from.
Also, if anyone wants some orchestral nostalgia:
https://www.youtube.com/watch?v=WG0htaa-Buc
A pretty nice orchestral arranged Golden Sun Medley. Sakurai and the devs need to pull more songs from Golden Sun's arsenal. Game has many incredible tracks!
Accursed
Hmm... that quake into move, and Force is pretty interesting. IMO, I think Isaac could work as a martial arts-ish kinda character and not have to use his sword directly at all, even for stuff like jabs which could be simple punches. The sword could be like a wand for some of his attacks, like the Ragnarok idea you proposed (the Flint idea for dash attack does sound pretty cool. Could be one of those rare times he uses his weapon, imbued with djinn energy). Otherwise, he could probably keep his weapon sheathed most of the time and fight by hand, feet, pysnergy, and earth to help keep him unique from other sword fighters. Anyway, really nice move list!
Edit:
IvanQuote
Wow, just finished watching that video. It was REALLY interesting. Thanks for the share!