Extreme obesity

If I could be assured of at least one dedicated care-giver (more than just an enabler, someone who would massage my rolls and clean me at least twice a day that is), and fairly solid health, I would be tempted.

Then, I'd say, under these circumstances I'd go for it.

For me, no. Two reasons:

1) I wouldn't want to not have had all the experiences with the world when growing up.
2) Even in fantasy, to me the element of options and choice are so key. Hugely fat and knows nothing else is not nearly as interesting to me as has seen life at various sizes and chosen go be hugely fat.

Bingo.

If you were immobile your whole life, I doubt you would find it as erotic as you do with it being a fantasy.