I've had the idea for ages, basically as a game conversion of the tentacle CYOA stories here on the forum. I think tons of pervs would jump on the chance to play that.
Missions would be capturing women for the hive out in the maze of a map. Depending on tentacle type and upgrades gotten, you could play stealthy, or bruisy, or tricksy, whatever. Hive would be your gallery/home base/shops, upgrades and stuff, breed some more tentacles. Could even do defense style missions where people figure out where all the women are going, if you cause a stir, or don't lose any tails on the way home, or leave someone awake to follow you.