iMore, which generally has good sources and a track record for accuracy, reported earlier today that the iPhone 5S will be released in August, according to its sources. It also said the next-generation Retina iPad could appear as early as April. Certainly Apple's plans could change, but as of now, this appears to be Apple's time frame.
So what will differentiate the iPhone 5S? iMore's sources confirm what other rumors have said: the next iPhone will retain the same form factor and will receive internal upgrades. iMore says these upgrades include an improved camera and a more advanced processor. It doesn't give any new detail on the fifth-generation iPad, but affirms past rumors saying it will sport an iPad-mini-like design with narrower bezels and a thinner, lighter body.
I hope this means it will sport an IGZO (indium, gallium, zinc, oxide) display. This new screen technology will be big news, and will clearly put Apple ahead of the competition. These displays are said to be sharper yet use up to 90 percent less power. This could mean a smaller battery, allowing devices to be thinner, lighter, and have an even longer battery life.
iMore says a new iPad mini might also be released as early as next month, but would likely only be a spec bump. A mini with a Retina display doesn't seem imminent.
Apple has been very predictable in its timing, generally releasing new models once a year. An August release for the iPhone would put Apple right on schedule, since the iPhone 5 came out last September. And April would make sense for the next iPad, since iPads have typically been released in April, with the exception of the fourth-generation iPad that came out last fall just six months after the third-generation iPad with retina display. But Apple was forced to break its cycle in that instance, because it wanted all its new devices to uniformly support the new Lightning dock connector.
Similarly, since the iPad mini first appeared in November, it seems likely that Apple will retain a fall cycle for the mini for any major upgrade to that device.
The big question remains: when will we see something new? Even if the rumors related to an iWatch and iTV are true, neither device seems imminent. I think the soonest we'd see a device would be late fall. That's because the supply chain is notorious for leaking details regarding component production, and we're not yet in that stage of the rumor cycle.
Apple also may launch a low-cost iPhone this summer, although that seems like an outside possibility to me.
Likely Apple's next event will relate to some online service or iOS and iCloud.