Google is apparently testing an updated Gmail interface that looks like a new mobile UI under development, according to leaked images obtained by Geek.com. And as we look forward to the expected Hangouts-Google Voice integration, there's a spot on the side of the potential new interface page for Hangouts—and it's collapsible.

The leaked images of the Gmail UI being tested by the Mountain View, CA-based media giant resemble leaks of the mobile Gmail UI. Aspects like marking important messages with stars appear to be on its way out, and this feature is being replaced with pins.

What's more, according to the leak, there are so-called "reminder creation bubbles" on the righthand bottom that "are nearly identical to leaks we've seen from multiple sources for future Google products, signaling a dramatic shift in how new functions are created within mobile and desktop apps," Geek.com says. "It's a simple UI tool that lets you store multiple unfinished messages or reminders in a sort of ToDo list if you are so inclined."

It's becoming increasingly clear that Google's 2012 acquisition of mail-client-maker Sparrow is beginning to pay dividends for Gmail's millions of users. At the time of the deal, rumored for less than $25 million, Sparrow's five employees were tasked with "new projects" for Gmail.

In addition to its mobile resemblance, the latest Gmail leaks also appear to give some credence to what we've heard about the so-called "Google 2" project. Ars noted last month that the "Google 2" project affects Google apps across Android, iOS, and the Web. Its goal is having a single design able to scale from wearables to desktops:

Consider something like the Android Fragments API, which is what allows the same app to power phones and tablets. In Gmail on a phone, only the inbox view is shown, but on a tablet, the app switches to a dual-pane mode with the inbox and navigation panel placed next to each other. Google has also been playing with selectable information density on the desktop, which you can change in Gmail just by clicking on the settings gear or by resizing the window.

Don't want to take our word for it? At the 2014 Accel Design Conference last month, Matias Duarte, the user-experience chief for Android, said "We need to stop thinking of 'mobile' as a distinct category." Duarte said desktop, mobile, in-vehicle, and wearables "should be considered as one design problem—as one product."

Among the leaked information, there was no estimated time frame, and it's not clear when a possible Gmail refresh will be released for public consumption.