We're starting to get a clear idea about what Apple has planned for the iPhone 7 (AAPL)

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Speculation is mounting that 2015 was the year of "peak iPhone." 

More and more analysts think that — for the first time ever — sales of the iPhone will drop in 2016, based on signs of weakness in Apple's Asian supply chain.

But even if it's true, the Cupertino company will still shift tens of millions of units — and launch at least one entirely new smartphone in the year ahead.

It may only be three months since the iPhone 6S came out, but there is an increasing number of rumors and reports swirling about its successor — some far more believable than others.

Apple hasn't even announced the iPhone 7, so it's difficult to be sure of anything. But here's what people are saying, and what to expect.

Here's what we know:

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For starters, there's a bunch of stuff we can be reasonably certain of. 

It's likely Apple's next smartphone will be revealed at an event in September 2016, and will go on sale to the public later that month. It's a formula that Apple follows like clockwork. That Apple now offers an "iPhone Upgrade Program" guaranteeing customers a new smartphone every year makes this all but a done deal.

That said, Apple Insider reported in November 2015, based on a "reliable source," that Apple is considering an earlier, summer release of the iPhone 7. It is, Apple Insider notes, a way "to help avoid a potential year-over-year decrease in sales as the iPhone 6s product cycle winds down."

It's also likely to come in two sizes once again. It was with the iPhone 6 that Apple introduced this twin phone model for the first time — the 6 and the 6 Plus (now followed by the 6S and the 6S Plus).

It allows the Cupertino, California-based company to target people looking for a big-screen "phablet" device without alienating customers who want something a little smaller.

It's been a roaring success: The iPhone 6 landed Apple the most profitable quarter of any company ever, and Apple says the 6S sold even better than its predecessor during its first weekend of availability.

Here's another no-brainer — It'll run iOS 10. Every year, Apple updates its mobile operating system shortly before the release of the newest iPhone. This then becomes the first device to ship with the new iOS version installed. In 2015, it released iOS 9, meaning iOS 10 should come out in 2016.

We also know that it will look very different (though not how it will look). Apple's smartphone works on a tick-tock release strategy. This means that one year the phone gets a big redesign and a new number (iPhone 4, 5, 6). The next, it gets revamped guts and a new feature or two, and an S gets appended to its name (iPhone 4S, 5S, 6S).

2015 was the 6S, which means 2016 should be the iPhone 7 — with a new look.

 

It might remove a whole bunch of stuff.

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So what changes will the iPhone 7 redesign entail? Piper Jaffray analyst Gene Muster thinks that Apple might ditch the home button altogether and incorporate a bigger screen.

"As many have speculated, the addition of 3D Touch may provide Apple with a way to eliminate the home button on the phone and use the additional space to make the screen bigger or make the device smaller," he wrote in an analyst note. "One barrier to this could be Touch ID, which is integrated into the home button currently. Apple would need to move the Touch ID reader to potentially the side of the phone to remove the home button."

Munster pegs the chances of this happening at 50%.

There are also reports circulating — originally from Japanese Apple blog Mac Otakara — that Apple is considering ditching the headphone port altogether. Right now, it uses a standard 3.5-millimeter jack.

That means there's only so much slimmer the iPhone could become: It's limited by the thickness of the headphone jack. But if it removes it altogether, it frees it up to shave off extra millimeters.

Be cautious about this one: The Independent notes that Mac Otakara has propagated false rumors in the past. But there's a precedent for Apple aggressively removing ports. In the most recent MacBook, it got rid of everything but a single USB port and a headphone jack— which is responsible for charging, connecting second screens, and plugging in accessories.

The change would also encourage people to use wireless headphones.

There's a load of new features rumoured.

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Home button out, headphone jack out. (Maybe.) So what's in?

Apple analyst Gene Munster thinks a screen upgrade is on the cards, making the device tougher. He reckons Apple could use sapphire for the screen of the iPhone 7, as "has long been rumoured." Apple already uses sapphire for the screen in some Apple Watch models.

Sapphire is extremely tough (hence why it's used in watches), so the change would make the iPhone less likely to shatter when dropped or hit.

There have been recent reports that Apple is looking to use OLED technology in future iPhones. But this shift is expected to happen in 2018 — for the iPhone 8.

There have also long been rumors that Apple is interested in building its own screen, but the latest report from The Electronic Times suggests that LG and Samsung will manufacture the screen for the iPhone 7.

Battery life is a perennial concern for just about every smartphone on the market.

As Munster says: "Another area on which we believe Apple may focus is battery life. Looking at Macs over the past few years, Apple has close to doubled battery life for its MacBook line up (largely 5 hour battery to ~10 hours). It has achieved this through more efficient processors and software. We believe battery life is one of the biggest areas of potential improvement and one that might be most welcomed by customers."

One of the wilder theories about the iPhone 7 is that it could be waterproof. The iPhone 6S is significantly more resistant to water than previous models — one YouTuber even left his two devices underwater for an hour to prove it. This has sparked some speculation that Apple could take it one stage further with the iPhone 7 and openly advertise it as a waterproof phone.

This week, a report from the Commercial Times claimed that Apple is actively looking into waterproofing the next iPhone, and is looking into using new "compound materials" as a way to make it possible.

Apple has also been granted a patent for "self-healing" technology that could seal device ports and make them waterproof. (Although not every patent the company applies for makes it into a finished product.)

And there have been high-end waterproof smartphones before, albeit not from Apple. Samsung's Galaxy S5 was waterproof. And Apple now has experience making water-resistant devices: The Apple Watch has an IPX7 rating, which translates into submersion in a meter of water for half an hour.

Thanks to the omission of the headphone jack, the iPhone 7 could be even thinner than its predecessors. Ming-Chi Kuo, a well-respected analyst for KGI Securities, thinks it might be the slimmest iPhone ever. In a research note seen by Apple Insider, he pegs the forthcoming device's size as between 6 and 6.5 millimeters thick — down from 7.3 millimeters and 7.1 millimeters for the 6S and 6S Plus.

The distinctive antenna bands on the iPhone may disappear, too. The unconfirmed report from Commercial Times claiming the next iPhone will be waterproof suggests that that the "compound material" Apple is apparently experimenting with could let it hide the antenna bands.

It sounds like Intel is building the guts of the device. In October, VentureBeat reported that Intel "has 1,000 people working on chips for the iPhone." At the time, the tech site said it didn't think the contract had been signed, but that it was looking likely "if Intel continues to hit its project milestones."

It could even track where you're looking. Apple has been granted multiple patents in eye-tracking technology that would let its devices use their cameras to see exactly what you're looking at and change the display accordingly — not displaying notifications when you're not looking, for example.

But Apple patents numerous ideas that never make their way into a finished product, so they're not a surefire indicator of what lies ahead for the company.

See the rest of the story at Business Insider