I think we should have this kind of seating in the game. My real life house has a window seat in the living room but I had to make it with tables and use the moveobjects cheat to get it looking right. Of course that means sims can't sit there. It's a shame. I'm thinking of putting seating in instead, but it won't look right as none of the sofas are backless.
Also, when I was a kid we had pouffes we used to sit on. Those would be fun, especially for kids and pets to sit on. We need backless seating!
Better to reign in Hell, than serve in Heaven.