Emporer is quite an interesting one....I for one think that will come to pass.
Evidence
Many may believe him to be the true heir to the (former) septim throne as a dragon born
Like who? Also, there's no way I can see that the Empire would allow an Emperor that wasn't an Imperial, let alone human. Considering the outcome of the war with the Thalmor, A High Elf would never be allowed for example. Yet a high Elf would still be accepted long before a Khajit or Argonion.
As for the logic of race etc
You never actually see them so they wouldnt have to worry about that
When talking about them they would just be referred to as "the dragonborn emporer"
If there descendants appear in later games as long as it is the grandchild or below (due to the Childs race being determined solely by the mother in tes) they could decide the race
That's about the worst work around idea I've ever heard. So basically they'll say that even though players might have had a khajjit character, because they had a nord daughter in law, then their grandson was Nord?
Not to mention, that interbreeding between the beast races and other races may not even be possible.
Plus, I've seen nothing that indicates that Dragonborn capability is even passed down generations or even related to the Dragoonbloods of the Septim line. After all, Neither Uriel or Martin used shouts, nor for that matter any of the line after Talos himself.