If you are enriching your child's environment, you are not going to stunt him even if you don't send him to any preschool. All you really need to do is to read to him, let him see you reading, talk to him, go places and see ordinary interesting things and talk about them and give him opportunities to play with other children his age once he approaches kindergarten age. Sing the ABC song, give him the opportunity to color and try to write letters, and read, read, read.
If you do that, you have no academic worries whatsoever. Some children learn very rappidly in the early years learning to read and write, and some learn slower. Some need special interventio to learn to read and write, but given what they need in school once it starts, they all pretty much even out by 4th grade and are ready to read and write to learn, so any early gains are not retainable. You just don't have to worry about this.
If you like the social benefits, go for it, but it is just not a necessity for most kids. Children with developmental disablities should start early with targeted interventions and therapies to help them over come challenges, but if that does not apply to your child, preschool is optional.
Your son won't be behind, not when it counts, so not to worry.
M.