It'd be cool to be able to create a really simple ARM-based laptop using a Compute Module from like Radxa or Raspberry. This would take some work to get hardware compatability working and the majority of the tools that are needed to run something like Fedora on an ARM machine should already be possible.
Taking from what I learn about getting a mobile RTOS working on an ST MCU I really want to be able to use that knowledge to create a framework for a simple open source phone. Why a framework-based design? Because I want a flip phone and Keet wants a slide-phone. If it's a simple framework instead of a set and done design we can have both and more. This idea would be for JUST a phone, however, I'd be interested to see how far it could go.
This is really difficult but building a custom ROM for my V10 to be able to use it as a portable media player because the DAC on it is sick. If I can do a good job of it maybe I could try other V-series models as well?
A self-hosted hub that let's you manage a personal blog via the AT protocol and maybe add connections for other protocols like Mastodon's at the same time?
A simple battery-powered BT keyboard that can be used for on-the-go. Maybe a foldable design, maybe a double-wireless design kinda like AirPods.