I understand what you meant by anyone with reiatsu is a potential shinigami but that only involves dead human souls. Ichigo is a born-shinigami or pure blood if i may say. They aren't in contact with Urahara so they can't possibly knows anything that he knows. Now what I really want to know is how does Rukia knows about Ichigo's Hollow? who told her? the only person to witness it in SS is Byakuya and he's not the type to go tell people about that. When Rukia mentionned the hollow inside Ichigo, Renji didn't seem surprised neither. Or is it more than meets the eye for that skull head thing that Ukitake gave Ichigo.
Now about the pace that SS is going, i agree that it is too fast. they should at least do some chapters explaining that or include it in the fillers or something. They forcefully pushed the characters(visiting shinigamis) in the real world witout sayin what kind of development SS is going. That is one of the Knock i guess you could say that i have on kubo, and it is the fact that he rushes the story way too much.