When you are talking about a 3 yo and rapid acceleration, I think you should think about how you can adapt social needs. I don't think recess with the 1st graders will really work, having just had a kid in 1st grade. They tend to cluster with friends, then eat lunch after recess.

You may consider some activity, like Karate, where he can develop age peers friends. I read 2 seriously PG kids, graduate college at 12-14 and they seem to have that kind of thing happening where they developed friends.

I don't see anything wrong with long term planning. Put the paths of the various outcomes and what the options are. But I don't see kids 3-4 years older hanging with your child as they get older. They are going to be into different things, and not discussing chess strategies.

Ren