Which, if one were to do such things, might slippery slope into doing away with the idea of race/species for the humanoids and just leaving a big menu of choices to pick from with point costs for everyone: breath weapon, tremorsense, wings, darkvision, skill bonus, etc... and removing them as separate entries in the MM.
Assuming slippery slopes are bad, the question is where in between is the happy point. Does deciding which are pseudo-species (Dwarf, Elf) and which are flavoring options (High Elf, Wood Elf) and making sure none of it has to do with culture work? Maybe put the pseudo-species hybrid idea in an option box and say some tables may like that, and if so, here's what the recommendations are?