Exploring bootloaders. Starting with GRUB, the Grand Unified Bootloader. It begins with a menu and has a console portion for examining the hardware and such.
Evaluate GRUB. There are two versions: GRUB legacy and GRUB 2. The second claims the first is messy code, while also essentially admitting to trying to be everything at once. Seems like neither is going to be easy to customize.
Would like software for exploring the hardware, in order to make a better decision of what software to activate. Assuming a specific operating system should be started is erroneous. An informed decision should be made by the person using the computer. That is just like when choosing an application, because that is essence what is happening.
Ideally, should be able to switch back to the bootloader to pick something new. Something like a game console that used cartridges. The computer would be like the console, and the external storage would have a list of useful programs, similar to a cartridge that had several games. Though, at first it would probably just start with a list of the known hardware, or a list of starting points tha could be modified. Again, sort of like a directory listing in dired.
Therefore, rather than switch between operating systems, switch between different programs for exploring the various hardware parts and their capabilities, or different groups of information or personal notes. Still deciding what is actually listed, because thinking that a list of options might ought to be brought up later rather than be primary, though a list of notes could be primary.
Would like to have it automatically pick a "native" resolution, or at least be able to change at request without having to reboot.
Likely will want unambiguous characters for the text. Look into fontopia for editing the font while in the bootloader. Being able to make changes to a font is actually a key factor to recording with a writing/reading system, just like with pen and paper.
Split screen for tiled views. Particularly for showing help and keybindings, so it can be read from one view for applying the knowledge in another view.
Saving customizations.
The menu at the beginning should be more like a directory listing. Never automatically activating one of the choices, because it might be started on different hardware than last time.