Some third-party manufacturers have added guest mode ability to their own devices - the LG G3 for example - but native Android still lacks the feature. The closest you can get at the moment is the guest mode via Google's downloadable Android Device Manager app.
The advantages of having a locked-down guest mode will be clear to anyone that's handed their phone to a friend or child to use for a while. You don't necessarily want them browsing through your personal data or having access to your credit card account.
By extension, parental controls could be tightened up with said guest (or child) mode as in-app payments or separate Google Play purchases can be disabled.
Going beyond that - having an easily accessible mode switch in the notifications menu allowing you to toggle between night and day or business and pleasure would be a nice touch.
More home and car support
By the time Android M rolls around we won't just be using the OS to control our smartphones and tablets but our homes, cars and wearables as well.
Google has already pioneered the Open Automotive Alliance and signed up the likes of Audi, Ford, Honda and Volvo. It's highly likely you'll be using Android M to pick your GPS route and music for the road before you've even got into the car.
On the home front, Google's acquisition of Nest could lead to some interesting developments by the time Android M comes along. Nest-rival Honeywell already supports voice commands, so there's potential for Google Now to be put to work again, this time controlling your home.
More tablet-centric apps
Compared to Apple's iPad selection, the quality of tablet-specific Android apps can be an issue - simply because of the huge amount of Android differentiation that's out there.
While the big-name apps are written to scale proportionally to different tablets, there's still a discrepancy between smartphone and tablet output.
Part of the reason this can be addressed with a newer version of Android is that we'll have 64-bit chips as standard by the time Android M is ready to roll.
With even mid-range devices packing the architecture - and ever more APIs - being released to developers, we're hoping for quality tablet apps once Android M hits.
Ultra power saving mode as standard
Faster processing, higher resolution screens and better multitasking all take their toll on battery life. Manufacturers like Samsung and HTC build-in power saving modes to their flagship models, but it's a feature we'd like to see Google incorporate into native Android.
Historically, the OS has been very good at showing you exactly where your usage is going but we have yet to see a single mode that limits all non-essential functions and severs data in order to preserve power.
It's a relatively simple extra that could build on Android Lollypop's battery saving function that, Google says, will give you an additional 90 minutes of usage.
Better native keyboard
It's been a long time since we've used the native Android keyboard because third-party options like SwiftKey are superior. Adding the option to set a third-party keyboard as default when setting up from scratch would be a useful shortcut.
While Google's keyboard gets the basics, like autocorrect and predictive texting right, there's more that can be added to improve the experience.
Themes, scaling and different key positions could all be employed for a more personalised experience.
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