That is some pretty high achievement. It sounds like your ds would be a good candidate for a skip and I'd be skeptical that subject acceleration alone could meet those needs. If he's not radically opposed to the skip, but just hesitant, I might push it a little with him. My dd wasn't opposed, but she also wasn't seeking it out herself. The school brought it up.
What we did was have her shadow a 6th grade student for a day at the middle school to see what she thought about going there next year rather than staying at the elementary for 4th. Perhaps if the school can arrange something like that for your ds, it might give him a glimpse of what it would look like and improve his opinion of skipping.
In some ways he sounds like my dd12 in elementary. She had "friends," but they weren't kids with whom she was really deeply connected and she was bending herself into whatever shape it took to fit with them. I think that, at the time, she didn't know what having real friends felt like. She is not skipped, but she has found a much better social fit in middle school for other reasons and I think now understands the difference as she has people with whom she fits without having to change or be someone she is not at the core.
