That's a laudable idea, but I worry about it branching out into unworkability. Coming up with combinations for nine base races is already a lot, and that number will only proliferate when you factor in the inevitable splatbook expansion (or even just existing races from 5E). Not to mention it leads to one wondering why it's only a one/one split; couldn't your half-orc have one parent that was a dwarf/human and another that was an orc/elf? What would that combination look like, in terms of traits?
The issue, as I see it, is that presenting the option of "universal interfertility" creates more problems than it's worth. The end result of that is that you end up needing some sort of table of racial characteristics, all with point values, and players get a pool of points to pick out their characteristics, after which they can define their lineage appropriately. And that leads to all sorts of issues, from game balance to expanded lists in new books to coming up with a reason why game worlds still have distinctive races at all if everyone's from a mixed background.
While less options tends to rub people the wrong way on general principle, keeping the game to the level of simplicity that the designers seem to want demands either an inelegant solution like the one presented in the OP, or simply sticking to the idea that most races can't interbreed, notwithstanding certain combinations such as the classic half-elf and half-orc.