There is a rather wide variety of people under the general umbrella of “growth fetish”, almost too many to list. The body part grown and the method of growth are both things that any game developer should hash out on their own, but the scale of the growth is something that also tends to be overlooked.
In an image or sprite-based game, increasing the maximum size can be an ordeal due to both screen size and difficulty of creating art, but in a text based game, size can be something as simple as a number. Increasing the maximum size of any type of growth can actually be incredibly easy if the growth was something that could be renewably triggered/collected to begin with.
Having stats with no maximum size is fairly simple as well. What’s more, if you want to give them unique descriptions for whatever “inspect self” method you have, it’s not really a huge ordeal to describe every size from miniscule to astronomical, as compared to all the rest of the writing in a text-based game. The larger the stat gets, the greater the gap between new descriptions.
Actually putting in methods to reach astronomical sizes is another thing entirely, but it’s my personal opinion that any text-based growth game that has repeatably-triggerable growth events should have near-infinite potential sizes and descriptions. Even if you do nothing with those sizes after a certain point (like immobility or bodily fluids), it can be a draw to your game to be able to simply go that large and still have it be described.
There are some who are turned off and disgusted by such sizes, though, and that’s entirely reasonable. If you’re worried about that, then include some way to toggle a maximum size. It shouldn’t be hard; it could be a setting, or if you’re feeling creative, let the maximum size be a form of skill or even a shop item (if you don’t want to be “unmeasurable” after reaching 2 meters wide, buy a measuring tape!). Of all the ways to accomodate multiple fetishes, simply allowing a theoretically infinite stat scale to become actually infinite is one of the easiest ways to increase the available demographic.
Two examples I have are Dawn of Corruption and The Curse of Something. Both have male muscle/genetalia growth as their themes (TCoS also has fat). They’re completely different games, but there is one aspect that TCoS does right and DoC does wrong: The descriptions.
In Dawn of Corruption, there are 6 total sizes for each size stat you can increase. Each stat’s actual value can increase to a massive size (they even covert it to miles at a certain point), but regardless of how large you are, the description is still the level 6’s “larger than melons” or whatever it was. It was the one disappointing part about an otherwise incredible growth game.
In The Curse of Something, there are 23 descriptions for the size of the same body part, ranging from 1.4 inches to the exact diameter of the earth. Each one is less than a sentence long, just a discriptor for how large it is compared to you and your surroundings, meant to be affixed to the end of a paragraph. Regardless, it vastly improves the game’s effect on those who are into such sizes, and it gives a lot more playtime for the simple reason that someone who wants to see the growth continue can.
Again, some people aren’t into it, but if you want your game to reach a larger audience, it’s quite easy to cater to those who are.