Breja: There are moments in Firefly and Serenity where things get serious, and Mal gets very serious indeed.
Fillion can act serious while he's standing still. He can act, no doubt. But to be Indy, you've got to be serious in the way you run, the way you move. Ford can absolutely do that, but Fillion moves like a comedy actor, even when he's trying to be serious. He's just fine with a gun (or space gun) in his hand, but that's not the Indy character. Even his most serious action bits as Mal - which to my mind are his interactions with the assassin - are either serious dialog before they start hitting each other in a tight frame, or quick gunplay. Like I said, bit of a Fillion fan, so I wouldn't particularly mind him getting a crack at the role, but I don't see anything in Two Guys, Firefly/Serenity, Dr. Horrible, or Castle that makes me think he's got Indy in him.
Is whatshisface a contender for Indy? Disney has the bankroll to cast Christian Bale or Matt Bomer or Keanu Reeves or really anyone as Indy. Or just sieve thirty thousand relative no-names until they find a perfect fit. Shame if they cast whf.