Sorry, I'm not a believer of time of birth and type of blood affecting personality and relationship success. Though I know there are people who do, I'll put forward a new idea.
A trait that makes sim act accordingly to their zodiac sign and blood type and affects how they get on with others depending on their's.
Though one thing I would like to see is horoscopes. Those can be fun to read. Perhaps display it as a notification and have it affect sim's mood a little (a lot if sim has that new trait).
When the zodiac signs based on time of birth are introduced, there must be a system where twins and triplets share the same sign. Plus it can be great for storytelling. Maybe when creating a family, some signs have the aging bar more filled up a little than other (depending on seasons if Seasons ep is owned).
However, the blood types are a different story. I only know the blood types in scientific way, thus I see those as genetic. It can get difficult if we can only choose O, A, B, and AB.
The thing is that when person with AB has a baby with O person, the baby can have either A or B-type blood. Now let's say that the baby's blood type is A, grows up and starts a family with someone with B-type blood (let's say their parents have B and O), then there would be all four options. Baby could have blood type AB, A, B, or O.
Thus with blood types, I'd make it so: you can choose two blood types for each sim: A, B, or O. If those two blood types are A and B, sim's blood type is AB. AA and AO for A. BB and BO for B. OO for O.
Then when two sims get together and have a baby, the baby can inherit one blood type from each parent. So when sims with AB and O blood have a baby, the baby will get either A or B from one sim and O from the other.
