What is one practical reason Nintendo should go one screen over two? You can't say because one will look better because they can toss two 540p screens in the and make it the same set up as 3ds. What are the gaming advantages of Vita over 3DS? Because last time I checked, I play just as complex and fun games on my 3ds as I do my vita.
I personally have no problem with two screens, but IF the handheld and console do in fact share games (popular theory), it would make sense for those games to be formatted to a single screen.
ETA: Unless there's a second screen on the console controller, which is possible.