To add: I had never heard of the "blueberry expansion" fetish before. But that sounds like it fits the above explanation. Five bucks says people with this fetish had a childhood experience where their parents sat them in front of a TV, put on "Willy Wonka and the Chocolate Factory", and went to make love in the next room. The kid probably figured out what was going on around the same time Violet Beauregarde turned into a blueberry.

There's probably a greater-than-zero number of people who had that experience, and there are probably similar fetishes around chocolate rivers, pneumatic tubes, and little orange people.

I've heard of expansion fetish before; my immediate hypothesis was that it's about mental wiring normally related to pregnancy (the same way foot fetishes are hypothesized to be related to wiring meant for your genitals). I've never heard of someone specifically wanting to be a giant blueberry but it's not hard to guess that once the general pattern of a fetish exists, specific details could be impressed by various conditioning processes.

I can't think of an analogous reaso someone might like chocolate rivers or pneumatic tubes. There probably are people out there who really like little orange people but by a totally different mechanism.