E.g., I’d like to have some wainscoting on the walls. You know, the lower half covered in some nice wood, the upper half just painted or wallpaper. Something like this:
E.g., I would like to have outer walls with the beams visible, like in some European houses.
I can even create the textures and normals myself (quite trivially), but I would need the game to use at least two colours for the wall: one for the wood and one for the rest of the wall.
I’d really love that 
plus basebords and ceiling strips (I googled these words, not sure about the ‘ceiling strips’ is there a better word?) the things along the floor and the ceiling of the wall
Indeed. Once you can have 2 or preferably 3 or even 4 materials for a wall, the sky’s the limit for what elements you can put on it. (Well, technically the ceiling is the limit 
)
As for the exact terms in English, you’re probably thinking of baseboard or base moulding (for where it meets the floor) and crown moulding or cornice moulding (for the part at the top.) But I don’t know what that translates to in Korean for Krafton, so a picture is worth a thousand words, and I thank you for providing those.
Being inZOI is still early access I’m hoping they at least have plans for the half walls with wood bottom halves with the wallpaper top and for walls with baseboards as well 
One can only hope, my friend. One can only hope.
Well more than one can hope
Roadmap 2026
Don’t worry, everything will be fine! With our help. The lower wall trim is called “paneling”.
I’m not sure what they’re referred to as in other countries, but here in the UK, we call them skirting boards (baseboards) and coving (ceiling strips).
We have two main types of coving. One is usually more traditional looking in appearance, and can be quite decorative and ornate in design. It’s usually made from polystyrene or plaster, and lined with paper for a lightweight option. You’ll often find plain and minimal styles using these types of materials too.
The other is what we would call cornice moulding. This would typically be made with plaster or wood, and can span across the whole ceiling, as well as the edges. This style can be very intricate in design, though it isn’t very common these days, and you’ll likely only find these sorts of designs in very old homes.
I will admit though, since I’ve been playing The Sims for such a long time now, I usually just call them baseboards and ceiling trim. 
Yes baseboards and moldings are correct terms, paneling is the wall part behind the wall trims
