As long as you stick with dual enrollment, everything should be fine as far as entering college as a freshman once he receives his HS diploma. He will likely need a HS diploma once he applies for true college entry (rather than dual enrollment). Don't do anything that would throw him into the category of a transfer student - that means limited merit scholarship opportunities. As for National Merit, don't discount that - while the true NMSC scholarships are only $2,500, some schools offer full tuition (or more) to NMFs.
I don't know what AP courses he has taken, but one way to extend the HS experience is to take a broad range of AP/honors courses. A little late for some AP course tracks now, but my older two (not accelerated or HG kids) both took two languages through AP. Middle kid ended up with 10 AP exams, five in STEM and five in the humanities. Often I see kids who have seemingly exhausted their possible HS coursework, really have only exhausted the STEM offerings.
