That's not possible with the lore stating that you get the racial appearance of your mother, so no matter how much you want hybrids hopefully they will never exist in the ES world.
One flaw, bretons. However, they were
centuries of semi-isolated breeding of nedes and aldmer, none of that 2nd or 3rd generation stuff. It probably required 10th generation at the shortest.
Also, can't really happen. There's already an Oblivion book, that's pretty much the devs saying in character, that hybrids cannot happen with noticeable traits. The child will inherit the mom's race, with
extremely subtle traits from the dad, and I stress extremely subtle.
So, if an orc mom and khajiit dad (if possible, currently dubious if the beast races can interbreed with mer and humans) had a baby, it would look and feel like any ol' orc to just about anyone.
If you REALLY want to stand out as a "mixed race" than select a race, and add some features that are not so dominate in that race. No one is stopping you.