I hope it will end up in creating a new system, where not only Shinigami will belong, because as it is, they simply are unable to keep up the balance with their numbers diminished to this point. Let's face it, everyone wants to see the formation of the Strawberry division for other species (Humans, Hybrids, Arrancars etc.).
The way it is, Quincy are the main enemy of Shinigami and Arrancars (which are partially Shinigami anyway, thus they are basically an embodiment of Quincy's hate). Thus it is quite likely that they will (have to) team up. This team up might even allow to create friendly relations in the future (remember that Kubo wants to push this story for another decade)... especially if the Arrancars Zan's can do the same things in their sealed state as those of Shinigami (you know sending spirits to other side, cleansing hollows and the like).
I actually wonder, if it wouldn't be possible for Arrancars to feed Hollows in HM with their own spiritual power, until they reach a certain level, were they will be turned into Arrancars, thus eliminating their need to constantly feed on helpless souls.
Dove tails perfectly with the consistent ideal held by everyone in Soul Society that Ichigo has brought change to an ancient Order. Having Ichigo be the catalyst that brings the entire Soul Realm into a new Era would be an ideal end for the manga.
"For I being a poor man, have only my dreams & I have spread them beneath your feet. Tread carefully, for you tread upon my dreams."