never say never. I would never dream of soloing Onyxia 3 yrs ago either. I've taken 3-5 shammies into naxx filling the DPS roles. Some fights seemed impossible to be boxed at the moment, Instructor Razuvious, Four Horsemen, Grobbulus, come to mind. I am sure with enough twick in your movement keys (key map with movement specifically designed for the encounter), and enough gear obviously, should be doable.

edit: impossible to be boxed at the moment just by yourself is what i mean. i.e. For Instructor Razuvious, you need to mind control two students to tank the instructor. Switching aggros back and forth, not an easie thing to do (box). But, with that said, I recently find that by running all 5 clients on 1 box. Individual movement was not as big of a problem as before when I run them on multiple PCs. mouse click and move is pretty fast. At least as fast as a slow keyboard turner. Again, totally possible in my opinion to solo box naxx, just not right now.