If I want more PC species, I can go to the SRD and there are lots of them, but if I am a collector, then I would rather to spend my money in sourcebooks style "Moderkainen's Monsters of the Multiverse".
I am not a true player, and then I can't say a right opinion about when the design of a PC specie is rightly balanced but I can tell my opinion about when the concept could be enoughly interesting. And other point is Hasbro wants PC species protected by trademarks to sell possible merchandising in the future.
Other option could be a recycled version of mythu'nn folk from Red Steel/Savage Coast, with some nerfing touch if this was necessary.
(half-)Tayfolk from Dragonlance could be interesting for one player with two PCs (who share a telepatic link)
Other idea is like awakened animals, but with some partial shapesifting traits allowing opposible dumbs to use weapons and tools. Ponyweres?