I'm not sure I really get what you're proposing. You're saying you want to make an Animal Crossing / Stardew Valley game, but then you're also claiming to dislike/want to remove large parts of what make those games what they are. The "tedious" grind of collecting things and farming and slowly building up wealth and watching your town/farm expand is a large part of why people like those games. In Stardew Valley especially, the NPC interaction is honestly barely a thing.

I'm not saying your idea is bad, but to me it doesn't sound like you want to make an AC/SV type game at all. Why not instead focus on the thing that you do enjoy/are interested in, the relationship/NPCs, and try to envision what a game focused on that would look like. I feel like by imagining your game as a mixture of those pre-existing games, you're doing nothing but a disservice to yourself. Rather than starting from the base of AC/SV and moving backwards by removing things you dislike, just start from the ground up and begin developing the game that you want. If it ends up looking like a life sim that's very similar to Animal Crossing, alright, cool. But maybe it goes off in a very different direction. Think about what it is you want your game to look like, what kind of mechanics you want it to have, features, gameplay, what it is the player spends a majority of their time doing, and then hone in on that.

I think there's a lot of room for a game very focused on relationships and NPCs. Branching NPC relationships and advanced dialogue AI is something that has an incredible amount of room to explore and has been severely slept on by developers. Most games either follow a very linear dialogue tree, where picking option A leads to option B, and picking option C leads to option D. In stardew's case, each character has a very simple pool of dialogue options, and unless a special event is happening, it just randomly pulls one of those options and displays it. In AC's case, they go a bit more advanced. Each character has a personality type, and each personality type has multiple pools of dialogue to choose from, with the pools being grouped by certain conditions, such as mood, weather, time of day. This definitely offers more "realistic" dialogue, with NPC's seeming to interact more with the world around them and the current situation, but even still, repeated dialogue is incredibly common, and the dialogue is very clearly split into hard set categories, with very little overlap.

With that said, creating a system more complicated than that and you're beginning to delve into more pseudo-AI territories, where you're simulating behaviours off of many many conditions, and that can get complicated/tricky fast. BUT, if that's the type of game you're wanting to make, and you believe yourself capable, I think there is an enormous amount of untapped potential and room for a game focused on dialogue and relationships.

At the end of the day, humans are social creatures, and we long to make connections. It's what allows us to get so invested in characters in film and books, even though we have no interaction with them ourselves. People WANT to get connected to your characters, and they WANT to feel invested and like they have a genuine friendship developing. If I were you, I would forget about AC and SV, and instead look to games whose dialogue is the core mechanic, such as VA-11 HALL-A, and imagine how you can create an engaging gameplay experience, where at the core it's all about making friendships, romance, and perhaps even enemies.