When a Shinigami dies where does their soul go? It must go to a higher soul society assuming there are tiers of soul society like Dante's Inferno where there are tiers of Hell(there does seem to be a hierarchy of power/position with a high demand of order which suggests there are tiers, and who does Yamamato take orders from?). In other animes they refer to an astral line where everything eventually returns to...maybe there's one of these in Bleach?
Now, if a Quincy isn't a Shinigami then is he/she Human? When Ishida's family was wiped out by the Shinigami did their souls go to Soul Society? If a Quincy has a naturally large spiritual presence then I would think upon death, IF they were indeed human, they would make super strong Shinigami. However, we haven't seen any Shinigami who were once a Quincy(but Soul society is infinitely huge supposedly and is rare for many to meet their former family there). So is it safe to conclude Quincys are not human and upon death do not go to Soul Society? If so, just where do they go?
If Quincys are not Human and are there own race ( i guess race would be a way to classify them), then IF a Quincy, like Ishida, were to cross over the hollow or shinigami line and then return to break down the invisible threshold of ones limits just as Ichigo has done...then would he be as powerful as Ichigo or maybe even more powerful?
Then again, it's just an anime and no plot is without holes.