I would not be surprised to see Jones get sent to the practice squad for Ray Calais. Calais can return kickoffs, has the hands for screens, and is absolutely lightning-fast (the Bucs special teams coach called him a "human joystick").
I have absolutely nothing against Jones; he's a hard worker and deserves a shot at the NFL...but we don't need five running backs.
Well to begin with please note that I don't think Jones is some amazing talent, he was a UDFA for a reason. But what he does have is a nice blend of abilities where he might be able to eat snaps and sub for "the guy" if required.
IMO the Rams keeping him was a mix of him showing a nice, well-rounded game (in particular the reports that had him showing well in his routes was good to hear), as well as concern for who will be the guy who can eat snaps and be someone they can count on for 2020. So if they do what you mention above then it will also suggest they are comfortable in that way with their top 3, that they think they have at least one guy who they can count on.
So that would surprise me for the reason that I don't think they're at that point yet with their RB room. I think we're going to see that unit sort itself over the first quarter of the season.
But then again what you suggest does make sense just from the perspective that keeping 5 RBs is crazy. Even if you count Calais as more a teams guy than anything else that's a lot of RBs.