Yeah the thing about RB is it's all about longevity. You really can't just be a 6yr type of guy, and at RB that is just harder than at other positions. Like a guy like Todd Gurley, imo could absolutely have been considered on that path, but his knees died on him hella young. Crazy that he only played like 6 seasons!
AP and Frank Gore are locks imo. Lesean McCoy and Marshawn are possible as far as recent-ish. Roger Craig, Ricky Watters, and like Tiki Barber could out of the older guys but probably never will...
But yeah I agree as far as currently active guys, it's mainly CMC and then a big drop off before Derrick Henry... and thats about it... actually the one sneaky guy that I think could get in is Alvin Kamara. It's weird cause I assume he would have to be like the first RB in NFL history to be a HOFer without every rushing for 1k! lol. Complete opposite of Frank who was a 12 time (pretty much) 1k yard runner. But he actually rates ahead of Henry in a lot of stuff. He's been racking up pro bowls, he's only trailing CMC by like 500 yards from scrimmage, and 4 less TDs, and they entered league at same time. He also hasn't had the major Knee injury CMC has had. But he's also never started a full season. I think he has a shot, even if slim.
If Nick Chubb hasn't had 2 significant knee injuries, I'd absolutely have him higher than Henry too. But that's a lot to overcome when he needs like at least 4 more seasons to make a real case...