Stafford isn't a lock for the Hall but I wouldn't say it's unlikely. Barring injury, there's a good chance he ends the season 12th on the all time passing yards list. If he continues to play into his late 30s (not a stretch) he should end up in the top 10 with a good shot at the top 5. He's got a good chance to end his career with more yards than Rodgers, Eli Manning, Marino, and Rivers. You mentioned Carson Palmer but he'll probably pass Palmer in his next game.
If Stafford plays into his late 30's there's a good chance he gets into the top 10 all time in TDs as well.
A lot depends on how he finishes out his career. Another 4 or 5 years of decent production (putting him retiring at 38) and I think he ends up in the Hall. If he gets hurt or collapses then he's on the fringes, probably left out in favor of all the other QBs of his time.