If they weren't considering upgrading the charge, I don't know why kidnapping would have been included. I suppose they could charge it as a separate crime without using it as an element of Capital Murder, but I'm not sure what the point of that would be.
To be honest, though, I think kidnapping in this case is far less obvious than murder. The case can technically be made, and probably should be, but I think it's more properly considered as a lesser included offense in this murder.
I hope it's tried as a Capital Murder case, although that's not what the current indictment provides. We'll have to see how this plays out.
I don't know about Texas, but in many jurisdictions, killing someone by accidentally running them over is not capital murder. Accidentally running them over and then kidnapping them to your garage where they proceed to die during the ongoing commission of the crime is.