The problem asks for the largest 2D shape that can be slid around a right-angle corner in a unit-width hallway.
Here is the perfect fitting sofa: https://en.wikipedia.org/wiki/File:Gerver.svg
That's especially easy to imagine with tables, but sofas also count.
There are also sofas that can be easily taken apart. Eg one of our sofas at home, an L-shaped sofa, comes apart into two pieces.
I would contend that it's still useful since you'd be able to turn the corner without over-complicating it by getting it into some weird tilt position.
That might give you a feasible solution, but I doubt it's optimal.