That Portal short is great - assuming we're on about the same one. Is there more than one? - so that'd be the shoe-in, I reckon, rather than trying to condense the complexities of the Half-Life universe. I'd guess that Abrams would produce, rather than direct, letting one of his Bad Robot commanders take the helm - Drew Goddard or Matt Reeves, maybe?
JJ Abrams, though... Not bad going from Lost to being THE go-to guy in Hollywood (behind Whedon, this humble fanboy submits).