First sensible rumour, i.e. isn't just guesswork, based on previous iPhone developments.
More pixels!
It's pretty clear Apple has to do something about iPhone's display. WIDELY under-reported in the Apple fan-bot universe, is how impressive the displays on competitor's latest phones were at MWC this year. Only the world mac journos ventured to ^truth^ that the iPhone screen hurt their eyes after viewing the new crop of competitors' phones.
I wouldn't be too disappointed if Apple had to increase the screen size to achieve this, either.