Falco should be in cause he's sweet...duh!
No but seriously the reason he should return is for plenty of reasons.
One: He's freakin sweet!
Two: He is easily tied with ganondorf as the most popular of the clones.
Three: Like ganondorf he plays an important role in his series and is quite popular.
Four: In the starfox series there is no one more popular than falco other than fox and on top of that out of your crewmates he is the only one around that makes you feel that you're not fighting alone.
Five: The guy is top tier for crying out loud and one of the most used characters in tournaments.
Six: Okay here's the long one: He and ganondorf are really the only clones that are truly different than their counterparts.
-Sure Doc's cape is a little different and he's slightly slower and slightly stronger. His pills have different trajectory, his f-air doesn't spike but instead knocks out and away (which if you watch the new trailers mario's f-air now does that). Other than that their the same.
-Pichu although he's a bit more different from pikachu than doc from mario(with moves being a little different), the fact that he hurts himself, is only SLIGHTLY faster than pikachu, is WAY weaker, and SO much lighter does not balance him from pikachu in the least.
-Roy is basically Marth with fire attacks. He is SLIGHTLY stronger, at least as far as damage goes, weaker in terms of knockback, his sword is more powerful at the hilt which sucks in comparison to marth's being the tip since you have to be closer, and he's quite slower than marth too. His counter is much shorter than marth's and so harder to hit with. It does return damage which is kinda cool but i think since marth's is longer and based off of knockback (somewhat) it's more useful. His airgame is also nowhere near marth's (plus marth's d-air can be used as a spike) and marth's repeated a attack that roy doesn't have is really useful. They made marth really good but when they made roy all they did was change marth around here and there, trying to keep it just as good, but ended up making roy which was just not as good.
-Young link is just a weaker and slightly faster version of link. I would argue for him if he wasn't almost exactly identical to link other than size, weight, strength, speed, fire arrows, a boomerang with more trajectory (less strength and distance) and an occasional d-air that spikes. I think link was fine the way he was. Making young link made players develop a style of playing with him that his moves were not originally intended for. Link is a power character...young link is a non-power player with moves that are for a power player.
-Now for someone I don't have to rip on. I honestly cannot find a single person alive who although they know ganondorf is captain falcon's clone, will say that he is just like captain falcon. Cause guess what? He's not! He's big, WAY WAY WAY slower, has horrible jumps, IS THE FREAKING KING OF STRENGTH and is as heavy as bowser. His moveset while it does somewhat remind you of the capt, is immediately noticable to be different. everything about this guy reeks of power. Hell, even his freakin jab is strong! It'd be nice if he was given more original moves but I really wouldn't care if he was kept as is.
-Now for the falco! A lot like fox and everyone who first picks him up says so. But after a few plays through people immediately develop a preference for one of the two. Why? Because they play way different. Falco's stunlazer vs. fox's rapid nonstunlazer, fox upsmash vs. falco fsmash, falco's d-air drill from hell, the difference in reflectors (the major thing), falco's longer reach, falco's higher jumps, fox's better recovery, fox's better speed, fox's up-b's flame's attacking, falco's over-b spike, falco using his reflector more for combo's as opposed to fox using it as a spike, and Fox kills upward better while falco kills outward better. Wow there's a lot of differences I named isn't there, and I know I missed a bunch too. But hey that's the same as what you did for other character's isn't it? Well Yes but the other character's were summed up much quicker and less complexly, while I have missed quite a few things about falco compared to fox. There a bunch of advanced techniques I missed too. The list I wrote outlining some of there differences just goes to show how many differences there are and why he is not like other clones.
Seven: The most important aspect is that in the hands of the player, you actually FEEL the difference of playing falco and ganondorf as opposed to the other clones. When I play the other clones I just employ the same techniques as their counterparts. (I just make sure to be more cautious with Pichu). With falco and ganondorf I play quite differently then I do with fox and captain falcon.
I guess you could say I like falco but I like him because he has earned me liking him because of the differences I noticed in him. I noticed these differences and then liked him not liked him so I imagined these differences to make him look good. I will honestly be disappointed if they don't put him in this upcoming game. Unlike the other clones (excluding ganondorf) he has a huge following that is rooting for him to be in brawl and would be upset if he wasn't.
Well only time will tell I suppose. Here are my opinions and you are free to argue them or play devil's advocate or whatever.