Sapphires have been around almost 50 years, they're not exactly a new mutation. They have been very resistant to improvement, however, and I'm currently looking into why that may be. I have a theory, but I need access to some equipment to see if what I think the gene is doing is what it is actually doing. Improvement in them may just be not possible beyond a certain point.
In my experience with them though... I have had 10 different sapphires here. I've had two that had a permanently leaking eye with no other related health issue (like malo or infection). One urinates up his belly instead of out and away from his body. One had a huge abscess but that was from an injury, not inherent health. One has had a high mortality rate in his kits. Most have topped out size-wise between 500 and 550g. One was pretty aggressive, one is high strung, but the rest of mine have been total sweethearts that sit in my arms and tolerate being petted, but that's on par with the chin population on the whole so I do not equate a sapphire's personality with its color. There is one that refuses treats (will take supplement, but nothing else), though.
I have not had any reach age 8 or older yet, the oldest one I've had here is now approaching 5.