Apple should make an external touch monitor for use with iDevices, primarily the iPhone, but also iPads. The iPhone 6s is very powerful — it performs similarly to the Macbook Air on some benchmarks. For years, I used a 386 with 4MB RAM running Windows 3.11. By comparison, the iPhone 6s is insanely powerful. There’s no reason it can’t drive an external monitor, for times when you need more screen space or a hardware keyboard. The iPad Pro is, of course, massively more powerful than an iPhone.
The monitor should be a touchscreen. Touchscreen are a good complement to iOS apps, which are designed for touch. It will be odd to see an iOS app displayed on a screen that’s not a touchscreen. Even if, hypothetically, all iOS apps were optimised for use with a non-touch screen, keyboard and mouse, since you’re used to touching iOS apps, the familiar UI will make you reach out and touch the screen out of habit. So it’s better to just make it work. That doesn’t mean you have to use it that way all the time. Just that when you do, it will work as expected.
Apps will have to be optimised for use on a big screen, adopting desktop-like layouts. They will need to have responsive design, because an external monitor can be plugged or unplugged while the app is running .
You wouldn’t have overlapping windows, which are complex and fiddly. You’d instead have a few predefined layouts to choose from, such as a single app fullscreen, two or three apps side by side, and maybe a 2x2 grid.
Or maybe an app, when it’s not full-screen, can have only one of a predefined  set of widths, each matching an iPad, like that of a
- landscape iPad Pro (10.3 inches)
- portrait iPad Pro (7.8 inches)
- portrait iPad Air 2 (5.8 inches)
This would let developers reuse their iPad layouts, and present users with a familiar layout if they also use an iPad.
The screen would be a standard 21 - 24 inches, rather than a big 27 inches. It will also not be a Retina display. The combination of small size and low resolution will have two consequences: one, the monitor will be cheap and two, it will have fewer pixels, so an iPhone will be able to drive it with good performance.
The monitor’s aspect ratio should be 5:4, which maximises the height, making it more comfortable to use with web pages or web apps. 5:4 doesn’t make it any worse for native apps, which will anyway have to have their layouts redesigned for a desktop monitor. Smaller monitors like 24-inch are constrained by their height, so a 5:4 aspect ratio is more important than it is on bigger screen like 27 inches.
When you plug in an iDevice, it will charge at full power (12W). The monitor will support USB type-C, Lightning , Mini DisplayPort and Mini HDMI. That way, you can plug it into an iDevice, 12-inch Macbook or other Mac. In other words, this can also work as a traditional monitor, without touch.
The monitor will come with a wired keyboard / trackpad combo — imagine a keyboard whose number pad has been replaced by a trackpad . There will be a single wire  going from the keyboard to the monitor.
This kind of monitor will hugely broaden what iDevices are capable of. For a couple of years now, smartphones have stagnated, and tablet sales are dropping. A touch monitor will let you do a wider variety of tasks on iDevices, and with greater productivity, or more fun. It’s overdue.
 If a developer wants to make an app that works on iPhone and iPad, they have the option of making one app that works for both devices, or two separate apps on the iOS app store, each of which is shown only to users of the respective platform. But with an iPhone that can be plugged in to an external monitor, you need one binary that can adapt to different screen sizes.
 We shouldn’t have too many sizes, which results in too much administrivia and fiddling rather than focusing on your work, and which requires developers to spend more time testing and fixing bugs in edge cases.
 USB type-C is reversible, standard and no bigger than Lightning, so the iDevices should switch to type C.
 Or it could be a separate trackpad.
 Or it could be wireless — Apple should make their wireless keyboard and trackpad work with the iPhone.