Succubus / Incubus and default form questions?

[Xarath]

So a succubus/incubus in default form is usually described as a demonic looking human, however is there also lust demons who appear as other demonic humanoids like orcs, goblins, elves even? I'm sure that Lust isn't solely a human thing right?

[UnArcaneElection]

Funny you should mention that -- most planar modifications of Humanoids (including both full Outsiders and Planetouched Native Outsider modifications of Humanoids)(*) are described as being modified Humans, with only a smattering of modified other Humanoids.

(*)For that matter, also most other modified Humanoids like Changelings and Dhampirs.

[Tarik Blackhands]

Generally speaking I'm fairly sure its implied that outsiders run the gamut of humanoid forms even if the typical examples are usually human or elf based.

One example that immediately comes to mind is in Hell's Rebels where the party walks into an old sacred area to Torag that's guarded by Legion Archons (as per bestiary typically 6-6.5 ft humanoid dudes) that are explicitly noted to be shaped along dwarf standards.

Goblin succubi are probably out there in other words, it's just most devs are going to default as they have because (most of) us humans prefer attractive humans/humans-with-pointy-ears to tempt us, not big headed pygmies with shark teeth and green skin.