I think you should do Boba Fett over Snake or Samus.
Boba Fett, from Star Wars is an amazing bounty hunter with a load of really neat equipment; a flamethrower, blaster rifle, thermal detonators, rockets, etc. It seems to me like it would be very possible to do as a PSA.
Check out Aafyre's ideas here;
http://forums.kc-mm.com/index.php?topic=15148.0Another reason to make this;
I am completely willing to make an accompanying texture if you or someone else is able to do a slight model edit. Using Master Chief over Samus, all I would need is the helmet to be edited to have a smoothed out front (and optionally the antenna on the side of the helmet).
Master Chief over Samus;
http://forums.kc-mm.com/Gallery/BrawlView.php?Number=5642example of Boba Fett's helmet;
http://images2.wikia.nocookie.net/__cb20090928215542/starwars/images/thumb/6/61/BobaFett-GH.jpg/800px-BobaFett-GH.jpg~~~~~
so ideally, a PSA over Samus would be great since a model is more readily available for making the texture. However, if a model is available for Snake or can be made available, a PSA could work fine over him too.
Personally I think another original character from an iconic movie such as Star Wars would be great; Boba Fett hasn't been done yet in Brawl, and definitely would be amazing because of all his weapons. Please consider this offer because I know everyone on the site would enjoy it.