I don't think the people who are asking for them to work on a new Golden Sun really understand what they're asking for here. They're just venting frustration about not getting Golden Sun.
Wayforward have a particular speciality and a particular House Style that is pretty set in stone at this point. They certainly have range as a developer and can work on lots of different types of games (that's what happens when you make a living as a Work-For-Hire developer!), but there's a certain brand of gameplay and visual style that they're clearly most comfortable with.
Wayforward is primarily a developer of 2D games, who generally prefer 2D pixel art and 2D handdrawn animation over polygons; though they're not averse to using polygon graphics where suitable. Their bread & butter is in 2D sidescrolling platformers, but are comfortable branching out into making other types of games with primarily 2D gameplay (be it top-down, side scrolling etc).
They have an affinity for Saturday Morning Cartoon style characters and settings (as well as tongue-in-cheek parody in general), and while they have worked outside that kind of setting before (Silent Hill: Book of Memories springs to mind), it's clearly their comfort zone. You wouldn't really go to Wayforward expecting them to make a new Eternal Darkness for instance, it's just not what they do.
Finally (and this could be said for western developers in general), but the "Japanese-style" RPG is something that's almost totally alien to Wayforward (Yes I know Sigma Star Saga exists, but that was a weird experimental genre hybrid of a game anyway). They are the last people I would expect (and quite frankly want) to be working on a new Golden Sun. It's just totally outside of their wheelhouse. It's Camelot's baby and nobody else could really do it justice.
Wayforward happened to be a great fit for Advance Wars, and I bet they'd be a great fit for Kurukuru Kururin too. They'd probably do a great job with some of Nintendo's lesser known and more lighthearted IPs, like Balloon Fight, Ice Climber and Startropics; but I wouldn't expect them to work on games like Golden Sun, F-Zero or Sin & Punishment, those genres and settings are just totally outside their area of expertise.