Remathilis
Legend
I instantly have a problem with that feat tax. I can pick elf AND have a level 1 feat, or I can take half-elf and use up my level 1 feat to pick it. Horrible, horrible idea that made people very angry during 4e. Feat taxes are awful..
I can't replicate my lore bard who had rapier and hand crossbow in 2014 without a feat tax. Or my elf diviner who used a longbow without a feat tax. There are some things that in 2014 won't be replicable in 24 without feats. Deal.
II would go with the option not listed. Put in the major ones. Half-elf, half-angel, half-demon, half-orc, and with human as the other half. WotC creates those individually to be on par with the other races. For obscure ones like half-loxodon/half-merfolk, there would be instructions in the DMG for the creation of half races and the DM with or without the player can just make it.
That's... what we have now. Every mixed species is essentially part human or genetically undefined, and you have race design rules buried in the DMG (heck, aasimar WAS the example!) and it's all up to the DM to allow, create and balance your elephant-fish person. Your vote is for the status quo.