We've reached monitor parity. We reached it because TV improved and there's no point trying to maintain a difference for difference's sake.
But the vertical height argument is just rubbish. People run 16:9 and 16:10 screens vertical all the time, and no one was ever going to be manufacturing giant squares which physically wouldn't fit on a desktop. 4K and the like is going to sell principally to the computer market first because lord knows there's little need for it in home theatre for most people.