lore problems aside. your thinking it wrong. there actually would not be alot of different pairings or w/e. im talking about it being like a slider. there wouldnt be a completely other option in the character creating menu for that crossbreed. in the character creation there would be slider for each race. were the slider is at is how much the blood the character has of that race. set imperial all the way up everything else all the way down you got a pure imperial. it wouldnt be any more complicated than an age slider no matter how many different options there were.
You're not getting just how difficult a slider of that magnitude would be to implement. An age slider does nothing more than tack on some numbered normal maps that give artificial shadows and 3D complexity to what would normally be a smooth face. Numbered normal maps can't display the gradual shape-changing between say, an Imperial structured nose and an Orc's nose (and yes, an Imperial's nose is different from a Redguard's nose or a Nord's nose; the face generation program has different base values and structures for all the facial settings of all the different races). In order to display the differences between the base structures of each race's face, you'd have to create some form of facial blend animation mesh, one for each pairing of race, to represent the gradual transformation from one race to another. It's worth noting that since you'd be altering the base structure of the face from which all other player-customizable face data is derived, it can't be done dynamically.
Your slider system is actually even more complicated than what I mentioned, because you talk about having a slider for each race, meaning you could combine blood from more than two races. Now, you're not only going to have the major hassle of creating facial blend animation meshes for each two-race pairings; you're going to have to factor in a third or fourth combination, again, exponentially increasing your workload.
And that's only for the physical shape of the face or head. That's not even counting textures. To account for textures, you're going to have to, once again, create some texture progression to represent the positions of the sliders. For each two-race pairing, there will have to be at least 3 or 4 different facial textures (and body textures) to represent the different combinations and percentages of race mixtures. Are you 25% Dunmer, 75% Bosmer? And if you are, should you look the same as someone who is 50% Dunmer, 50% Bosmer? And just as with the meshes, the amount required becomes exponential when you factor in a 3rd or 4th racial contributor.
And then there's the differences in the structure of the normal maps used for the age slider. Changing the facial structure via that facial blend animation mesh means that the stock 10 sets of numbered normal maps aren't going to fit the face correctly. Which in turn means you've now got to do the same thing here as with your textures. Except they have to perfectly follow and fit however many "stages" are represented in the facial animation meshes. And again, the workload increases exponentially the more racial contributors you add.
You can't just declare a slider and say, "I want it to magically blend my races" and have it be so. There's a [censored] ton of work and effort involved to provide the resources to give that slider actual meaning and definition.