I'm currently trying to implement a 'birth sign' system, kinda like in the Elder Scrolls games. Searching through the scripts I noticed that essentials keeps track of moon phases and astrological signs in the zodiac...seems like a waste to have that just sitting there, not really affecting anything.
So far I've been able to make it so that the game will recognize which 'sign' a Pokemon is born under, and I've put together some graphics to accompany each sign in the Summary pages (coming up with constellations and lore to go along with them). I've written out some basic ideas for bonus effects each sign will bestow onto a Pokemon, but I haven't implemented any of them yet...so at the moment, it's pretty much just novelty.
I think if I combine this with an Unreal Time system, some cool bonuses, and link some kind of quests and things to it, it could really deepen the breeding system and help personalize your Pokemon a bit more. I'm also thinking that something special can happen on your Pokemon's birthdays, or maybe they get some kind of additional boost if you use them during times of the year that correlate with their birth sign. I think there's lots of potential with this idea, I just hope I can figure out how to properly implement it beyond just cosmetics. I'm not a coder or anything, so everything I've done so far is a gradual process of trial & error.