Step 1: I think here maybe the default setting should be solarized-dark/light on terminals. It's honestly a good and sane default. It's purpose built to be less hostile on the eyes in my opinion, which should likely be what's aimed for in a default setting... the themes and colors are there for people who like to stare at their terminal all day (if you only use it once or twice then you don't care about what color it has) so it should be eye-friendly defaults. if people want to muck about changing it to their own custom theme they won't be bothered about defaults anyway since they will immediately customize it.
I personally hate the fact I even need to swap a theme, or download and reformat some Xresources file tediously (while looking at godawful colors in the process!). I just want my eyes not to burn.. don't care what colors yield that result.