Glad to hear you are enjoying the game. We do pride ourselves on the character first approach to the fetish story telling, so we always appreciate hearing that it resonates with the audience.
At this time there are no current plans to add additional fetishes to the game. The growths themselves are confined to certain things (for instance they grow existing parts, not just entirely new things) and they are confined to just one type of growth (for instance, hourglass and strongfat are technically two growths). Though there are other growths mentioned in the game (hair, lips, nips, nails, feet, and other "appendages") these are really just for the tertiary characters. The time constraints however, are really the biggest obstacle. The game has been in development for quite a while and it has been difficult to keep pace with demand for new content as a completely volunteer project.
However, that's not to say ambitious and motivated artist and writers can't craft their own OC's that occupy their fetish. The Mika mod is a good example of this https://gamikamod.itch.io/growth-academy-mika-mod