I actually really like Schwartz's idea of Drew Goddard...better, in fact, than Joss Whedon, even if he was available, which he wouldn't be. Whedon's too distinctive a writer, which sounds mean to Goddard, but I think being able to adapt yourself to a particular pre-existing style is a talent in and of itself too.
I really think the best likely name being floated, however, is Brad Bird. He sounds somewhat occupied, but come on, if Star Wars comes knocking...
Martin Campbell would be a good choice, too, I think, Green Lantern or no Green Lantern--I think that movie suffered from executive indecision. He really knows how to do solid, propulsive action storytelling, which is, I think, crucial for Star Wars, plus of course he's already meshed well with one big-name franchise. Jon Favreau is a good suggestion, too--he's shown himself to be good at bringing humanity to blockbusters, which is something Star Wars desperately needs, and I love his philosophy of using all different varieties of FX tools, not just wall-to-wall CGI.
You know who else I think might make an oddly good Star Wars director? Edgar Wright. Admittedly he's a pretty distinctively berserk stylist, and would probably have to tone it down a bit...plus as a few people have been saying, I'm not sure I want a really unique and creative filmmaker to be wrapped up in Star Wars instead of making their own flick...but getting him to do one movie just somehow feels right. Probably won't happen, of course (though doesn't Wright hang out with Peter Jackson, who in turn hangs out with Spielberg? Seems like he's in the right circles to at least be considered...)
As for Arndt, I loathed Little Miss Sunshine, but I do feel like he might be right for this. Star Wars doesn't need a Charlie Kaufman, it needs someone who can write a script with really really rock-solid structure and momentum, and I have to admit LMS had that. This could be a Paul-Haggis-writing-Casino Royale situation, where the guy's a complete hack when he tries to produce "prestige" movies but has a grasp of fun pulp.