Remathilis
Legend
How about a compromise: Put them in the DMG as examples of how a DM can combine two different species traits to make new species. Then the DM can use them as examples if they want to make other hybrids for their game.Which is why I think having the core book include half orcs and half elves works. Those have been tested over time. Other options can just be in optional in supplemental books or ruled in.
I would probably still rename them in either case.