I doubt it.
For a small device such as a phone, 16:9 still isn't that much different from 4:3 that it will look or feel awkward to use.
However, as the dimensions increase, the disparity in length will become all the more apparent. I would probably end up sacrificing way too much width to be able to use landscape properly.
Even on my 27" imac, my browser rarely takes up the full screen. Usually, like 3/4 of the length, with the remaining space for video and other folders. Maybe if the next version of IOS allows some form of multitasking or multiple windows open at the same time? I don't mind being able to say, surf safari while watching a video and having imessage open at the same time.