Was just replaying the end of Skyrim's MQ the other night and something about Alduin in Sovngarde caught my attention.

Alduin has always been known to eat the current Kalpa, recycling it and rearranging it to start the next Kalpa. In Sovngarde, Alduin casts a soul-snare across the spirit-land to capture and eat the souls of the dead. If we connect the two, then that would mean Alduin is also recycling the souls that he eats, essentially fulfilling the Dreamsleeve's soul-recycling function.