Yeah if I'm creating a game where mix heritage is a possibility and a thing then I would design my species that it would be easy to figure out which traits would carry on in a mixed species.
Personally I will go to next step further and make each species have a category (Mammalian, Reptilian, Constructed) and only let species of the same category mix. Not dragonborn/elf mixes without magic.
Then label traits as dominant. A human's feat or an elf sentence might be the dominant aspects.
Or if that is too complicated just make stuff species and then list which subspecies are brought about by mixtures. A Dwarf and Halfling creates a stout Halfling. Orc/dwarf, human/dwarf, and Goliath/dwarf are all multiple dwarves.
But this goes to the main point
D&D considers half elves and half orcs is important aspects of the core game, therefore they should be an SRD.