Actually, Motoi Sakuraba was the music composer for Dark Dawn as well. He might not have been mentioned on the composers' page to keep the inclusion of Isaac a secret but he did compose for DD as well.
Golden Sun is being especially hidden from our eyes but this CAN be really good news considering they might have a GS4 game in the planning or even GS1 and 2 remake! Although I doubt the remake since they already released the 2 games on VC but still, I would definitely buy it! Or maybe even GS4. Golden Sun's formula is not broken up but Camelot was unable to use it to its advantage as well as the built up plot to make DD, thus its lacklustre sales as well as lukewarm response.
Maybe we can see some small changes to make the game even better and perhaps more strategic! Plus a plot to fix all the plotholes and loopholes we have gotten so far. Also a GS4 on Wii U......
It is true that Xenoblade was also kept pretty hidden and we saw no indication of it except the composer list included it as well as all the leaks mentioning Shulk. Granted Isaac has not been shown in many leaks, I have seen only 2 rumours with him but why not? A character does not have to be in a leak to get a spot and Isaac's popularity as well as legacy is enough to warrant him a spot, not to mention the amazing potential he has to bring something new to the table that no other fighter has, EVEN after Robin and Shulk's reveals.
Here's to Isaac in Smash! Buck up everybody, not much time left. Unless Nintendo does a wacky move and not all characters are included on the 3DS cartridge from the get go....