would have to be fully open source hardware and software and to be totally disconnected unless I used an external device to connect it while I was wanting it and could disconnect it at will such as Bluetooth for example. Also, something tells me that something like this should be nothing but a dumb pipe and have the computing outsourced to an external device such as your smartphone simply due to the fact of hardware upgrades. Somebody farther down in the comments mentioned not wanting the equivalent of an iPhone 1 in their brain and have to switch it out all the time and so a dumb pipe would fix that because the computing hardware would be external.