Yeah, it wouldn't be THAT hard to create a moveset for Alex. For those who have played the Golden Sun games, you know that there are virtually no unique abilities for adepts (for outsiders, the characters in the game able of using "magic" a.k.a. psynergy) with the exceptions of drastically different characters in the same element (ex. Jenna (weaker, female, caster) and Garet (big, strong, warrior, also see Mia/Piers) carry different moves). So, seeing as that is, they could draw on any mercury (basically, water/ice) technique to use for Alex, and perhaps develop a new move or two. This isn't nearly as much of a stretch as many of the characters that have been put into Smash already.
Alex also has a much better chance of making in it Brawl compared to Mia. First off, the most obvious issue is that Mia's main purpose as a character was to play the role of healer (this is not only based off of battle styles, but her description and character development in the games). This creates an obvious difficulty in designing a character, especially when the most obvious specialties of the character are extremely broken (healing is very rare and/or situation in every smash game). Alex, though not much was shown, is much more obviously an aggressive character, who's role was PREVIOUSLY as a keeper of Mercury lighthouse, but his lust for power (and other reasons, trying not to spoil the game) lead him to go on his quest, which struggled against the main characters of the game (more so in GS1 than 2, but you get the idea). Furthermore, Alex is a villian which Smash clearly needs more of. Finally, he is pretty much the second most important character in the series, coming in behind Felix, and definitely ahead of Isaac...(arguement following)
NOTE: SPOILERS AHEAD, if you still wish to read please highlight the text.
Okay, in Golden Sun, Isaac was the main character in the first game, but he is not as important in the series as either Felix OR Alex. If my memory serves me correctly, Isaac is attempting to prevent Felix and Alex (along with other characters, more on that later) from lighting the four lighthouses (1 for each element) as he was told by the Wise One (a floating stone who seeks to "guard" the element powers, so to speak). Now, towards the end of GS2 you find out that Felix and Alex (who has other motives) sought to light the lighthouses to unleash the power of alchemy upon the world (in the game, a strong magical power) and prevent the world from slowly falling apart, which they find is happening. When Isaac learns of this, he seeks to help Felix continue his quest. This right here shows his subordinance to Felix once he learns the "correct" path. Therefore, we could surmise that Felix is the true main character of the series, at least in the hero department. Now, Alex is never a playable character, but he makes frequent appearances to either hinder Isaac or help Felix, as well as pursue his own desires. However, he is not heroic because of his reasoning to light the lighthouses. He disguises this with his desire to save the world and unleash alchemy, but his real goal is to achieve ultimate power from the Golden Sun (hence series name) making him the main villian of the series. Now, here's where things get a little subjective. Alex is the more important to the series than Isaac because of how he plays. Once everyone learns about what unleashing alchemy will do, there is no doubt from anyone that they must finish the quest. This makes the entire series turn out to be just an entire struggle (against, apparantly, nothing) to save the world. Alex provides the black in the plot, he is the contrast of the good. Without Alex, there is no evil in the games, it is all just one big fight against random monsters for good. Alex brings villiany. Alex brings chaos. Alex brings DEPTH. Isaac ends up just being a strong warrior who helps Felix. Jenna, Sheba, Piers, Mia, Garet, and Ivan all deserve a spot as much as Isaac as they serve the same role in the series. Therefore, Alex definitely is more important than anyone except (arguably) Felix, who I would put on an even level.
Kal aMari: Unfortunately, as much as I would love to see Saturos, Menardi, Agatio, and/or Karst in Smash Bros. this would be impossible as they are dead. That would seriously hinder their ability to appear in a super smash game.
So, pretty much I would like to have Alex and Felix representing GS in Brawl.