A rich console-based git client. Think Midnight Commander meets GitExt.
Devs are split in two rough categories: hard-core console users who do everything from the command-line and who are missing out on nice merge graphs and other gui-friendly tasks, and mouse users who are forced to switch to the console for advanced commands. Both groups would get an improved experience from a unified client that seamlessly transitions between those two modes.
Midnight Commander is a great example of an application that mixes a rich, but text-based experience, with the unrestricted power of the command-line.
Similarly, MidnightGit will show a rich view of your repositories, with fast access to the most common tasks, and unrestricted access to the command-line at all times.
Also, having a client that easily works over an SSH session would rock.
Of course, it will be cross-platform and low-friction to install.
I literally thought about this this morning (2/27/2018), so not very far at all, just getting excited with the idea and thinking out scenarios and features.
I'm sure somebody did. Googling it found this, for instance.
Let's just brainstorm there for now.