I'm sure Data wouldn't be a big issue.
imo it will have to be a morph system to work without being a complete resource hog. Otherwise the other way would be having completely separate meshes for all body types, and the complete library of outfits having matching versions to accommodate them.
If it was just used to give different weight representations, you would only need to store a morph target at the highest possible weight, fat. then a value in the npc and character could be used to morph to any point 1-100% towards the morph target. giving the
further more there could be a system where you have texture blending in morphs too. so as the morph slider rolls up towards being fatter, the texture blends.
something like this is still resource hungry. even baring in mind that the body asset isn't all that is entailed a character on screen, it's still basically doubling the resources needed per body
It's down to how much they can pull in from other areas.
Instanced geometry and some culling features i imagine, if implemented, give them some more room. probably quite a bit seeing how much is usually going on on screen in a TES game.
I'm hopeful but not confidant.