We've seen the first "bendable" displays hit the market over the past year. We've had the LG G Flex, the Galaxy Round, and the Galaxy Note Edge. I think that we're slowly moving towards bendable, retractable screens, and that will make the screen size a moot point (as the object you carry in your pocket would be significantly smaller than it is when you pull it out to use it).
But until that happens a few years from now, screens will continue to get bigger. Last year, 5" was the standard. This year, it was 5.2". Next year, it looks like it will be 5.5". I think we'll ultimately make our way up to about 6-6.5" before the bendable screens end the "size wars" for good.