I feel like if you're so concered about your kid being "bored," then maybe his preschool just isn't a good fit. But it also seems concerning that he mainly plays by himself-- he probably would actually benefit more from another year of preschool so he can have the opportunity to work more on building friendships and social skills and just being a kid. If he's bored and doesn't really have friends, I'm not sure pushing him into kindergarden is the answer he needs. And academically strong or not, a competent evaluator will note those traits as not being kindergarden ready.