B.,
You should be prepared to face very difficult times ahead. Just because someone's neighbor's cousin was like this and is now an honor student does not mean that this child will do the same. It means that some kids do, and those people talk a lot more than the people whose kids continue to fall behind. The truth is that delays are a giant red flag and chances are good that he will have more delays than you see at 9 months. He has loads of developmental mile stones to reach in the future, and the best indicator of his future development is his passed development. Early intervention is his key, but that may only help, not cure him.
You need to know what the cause of his delays are. If he is just slow to develop, that is far different than developmental delays from autism, fetal alcohol syndrome, prater willie syndrome, or many of the other things that could cause this.
To get the kind of information that you really need to make a decision of this magnitude, you need to see a developmental pediatrician, neurologist, occupational therapist, physical therapist, speech and language pathologist, and a geneticist.
If it really makes a difference to you that this child be typical in the future, then he may not be the child for you. Take very careful inventory before you adopt; you are questioning for a reason, and you should be absolutely sure why this is nagging you before you adopt. I urge you to get accurate and complete information from experts first and then search your heart with the worst case outcome instead of the best, just in case.
M.