sorry, I didn’t mean Naga tails, they are legs, I meant Frostwyrm tails and Gryvain tails, which aren’t legs. Since it describes them as being as thick as the owners waist at the base, it wouldn’t really work to have multiple of them.
Strictly speaking, it's already possible to have multiple gryvain tails; the DracoGuard TF that reduces tail count to 1 is separate to the TF that changes tail type to gryvain. That said, the Appearance screen doesn't match that and always describes gryvain tails in the singular. The weird thing is that frostwyrm tails are in the exact opposite situation; the Frostwyrm Ichor TF that reduces tail count to 1 is the same as the one that changes tail type, but the Appearance screen still accounts for the possibility of having multiple frostwyrm tails.
For reference, the tail types that the Appearance screen supports multiples of are: canine/doggie/lupine, korgonne, demonic, bovine, sheep, feline, lapine, vulpine, cuntsnake, red panda, raskvel, badger, vanae, ovir, cockvine, simii, tentacle, frostwyrm, xhelarfog, saurmorian and hyena. This is based on the current public source code which is months out of date and thus doesn't contain zaika tails, but with the existence of hydras I assume multiple zaika tails are also supported.
The ones where multiples aren't supported in the Appearance screen are: equine, drider/arachnid, bee, myr, shark/siren, lizan, avian, kangaroo, draconic, gryvain, kui-tan, deer, mouse, panda, frog and swine.