More dialogue for the characters! And the ability to change the player's name is a must. "Null was impregnated xxx times." Also, a character select to start would be nice; pick a base race, and go from there. More furniture! That's a big want, furniture. The ability to walk around your machine would be great, too - just an overhaul of the design would be very much appreciated. ^///^
But the big thing here is just more dialogue and lines. Especially with your partner!
A small request would be a dominant/submissive switch, and a way to build Heat for certain characters. Like, a pheromone humidifier, which you can choose which rooms it'll pump to. The dominant/submissive switch is used to specify what positions the character will default to when in heat. Dominants will want to be on top/giving, and submissives will be receiving. It can have a default option based on the characters as they are now. And of course, their favorite position will have double the chance of popping up.
A story would also be great! I get strong Undertale vibes from the combat, too.
Growing towns would also be great. From village > town > city.
Split paths when digging! Sometimes a hole just needs to be a little deeper. Maybe you could add levels to mines, with harder enemies/more materials the deeper you go?
Music!
And a very important one: Duration boosters, and performance boosters. When used on a character, a duration booster will increase their HP by 100, and reduce their Tech down to a minimum of 0/11/22/33 (depending on level of the booster) for sex only, until you turn it off. A performance booster will do the opposite - while it will still grant 100 HP, it will also grant 25/50/75 Tech for sex only. Also, a Tech Limiter and an HP Limiter both would be great. Each will limit Tech/HP in sex to the number you set. So you could have 70 tech and 100 HP, without blowing a ton of permanent stat changes on the character.
This is a great game so far, I love it! Keep it up~