So I am planning to create an animal farm soon but it kind of made me sad that you don't really earn much from it than crops without bugging/slowing down your game. I was thinking about it and I'm also currently playing SOS if you're familiar with it. They have this increasing byproduct amount and level. Increasing byproduct amount will, from the name itself, will increase the amount of byproduct you get everyday so instead of 1 egg or milk or wool, you get 2 or 3 or 20 instead depending on the byproduct amount of that animal. As for byproduct level, we already have this with SV where it depends on the affection. So what if we can add the byproduct amount to SV to make animal husbandry more profitable and fulfilling. We can add another meter (or invisible meter) for byproduct amount and we can increase it by giving special treats for animals. I don't know if this is feasible or there is already a mod like this but hopefully, someone can make or teach me how to make it.
You should probably join the SdV discord, there's a modding channel there where folks can help you out if you really want to make a mod. It will probably have to be a Smapi mod, given what you want to do, which means using C#. (It does sound like an interesting idea)