certain NCL and RCCL ships have them.
i think NCL's may all be interiors, but i'm not sure - from what i understand they are often centered around a lounge area so the solo travelers can meet each other.
royal has interior, ocean view, and balcony. i've not stayed in one, but i did see a balcony one on quantum/anthem of the seas, and although it was small, i was actually surprised at how spacious it seemed. it was missing a couch (had a small chair/stool instead), but had a normal-size bathroom, bed, desk, storage etc. on that particular one, the balcony was ginormous, too - it was on a bumpout area so very deep. i wouldn't think twice about staying in one.
ncl and royal rooms are generally smaller than disney category-for-category, but to me it feels like so much space is taken up by the split bath on disney that the actual living space in the rooms is about the same. others have said they definitely feel the size difference, though. i think a lot of it depends on configuration, storage, furniture, etc and not so much on actual square footage - i mean, unless you're in a big suite, all cruise rooms are small.