Board Thread:Lore Discussion/@comment-72.77.73.35-20140408131341/@comment-69.123.217.197-20150211013112

I believe it's been mentioned above in some capacity, but I figured that the Last Dragonborn was exempt from the "normal rules" regarding souls due to the fact that he/she is a dragon. Dragon souls are not ordinary mortal souls, and cannot be claimed in the same way. Note no dragon can be soul trapped, and even those that are trapped in oblivion planes, Durnehviir and Miraak, are simply physically trapped there: the Ideal Masters do not "own" Durnehviir's soul, just as Hermaeus Mora does not "own" Miraak's soul. Durnehviir has simply lived in the Soul Cairn for so long that his physical body cannot survive outside of it for very long, while Miraak is simply trapped in Apocrypha with no good exit.

Dragon souls are bound to their physical shells after death, thus why Alduin can resurrect the fallen members of his army, unless there is another dragon present at the time of death to take ownership of that soul. In addition, by very nature dragon souls are somewhat divine, as they are shards of the Time Dragon. Considering the fact that the Last Dragonborn can quite possibly consume thousands of dragons by the end of his/her life, I would reckon that they would at the very least be able to simply go to whichever afterlife they preferred, if not transcend to godhood by virtue of having such a large soulstack.