Understanding that the game is hardcoded to only allow 13 races, and changing the races themselves requires modding...., I suggest adding a few options when customizing race, outside of modding.
1) Add in 'Racial Focus' trait selection, whole new panel. Basically, so that instead of modding to open them all up from the get-go, you have the choice of
Organic: your race has focused on organic technology to this point(sets racial available starting propulsion type to organic engines and power source)
Doesn't lock you out of anything, and I would hope that graviton isn't a choice since it is, after all the best(but you could
make this panel moddable so people could mod graviton focus as a choice.....)
2) Add Empire logo choice - click on the logo when customizing race, and a popup window with available logos(from a pre-set folder? so adding new ones becomes a breeze) shows up, allowing you to select the one you wish to use.
3) Add Empire border color choice. Simply put, I'd like to use my favorite color no matter what race I play. Probably need to set the AI to use:
If PlayerUsing DefaultColor=False Goto UseDefaultColor
If PlayerUsing DefaultColor=True Goto UseRandomColor
UseRandomColor Allows Reuse=False
added in there
I guess this list kinda ends up being suggestions for horizon 2 even in the ones above, but definitely for the next two here....
4) Click on Race Portrait, get a popup to choose race portrait from preset folder's available options, much like empire logo
5) Probably need a whole panel for this, with a selector on the left, and a preview on the right.... Player Fleet Choice: Allows you to choose which pre-installed Ship 'looks' to use from a preset folder. Probably end up with a subfolder that looks much like Fleets: 0001, 0002, 0003, etc. as subfolders.
Most of these would probably require coding the AI to use a default choice, unless in use by the player, in which case they choose at random, for every option providing it isn't in use by another player(AI or human) in the game.