My now 4.5 yo was the same at 3. Truth be told, everything we did at home, just continued. I only have him in preschool 3 days a week, 3 hours per day and he is increasingly bored and having behavioral issues (due to boredom, sensory issues and executive funtioning issues). I probably should have kept him in the 2 days a week program. He always tells me how boring it is. He loves playing with his friends and playtime is his favorite part of school.
We are currently in the process of entering him into K at age 5, middle of the year. We are in CA and it's unheard of at this time, but I have taken our mission all the way to the superintendent and the school board.
We are also considering a homeschool program as an alternative if public K isn't working out. It's a m/w/f at home learning schedule and they offer t/th enrichment courses.
Around 3.5, our DS began to draw and paint and art was a new obsession. This was a great replacement activity to academics, which was his first love from 12m-3.5. His interests began to change and he started playing with toys more. I got him an electrical circuit at 4 and other science toys as well. He still enjoys workbooks, but not for 4 hours straight. We also enrolled him in a music class (music theory not a group sing-a-long type). I take him to our local children's museum almost two days a week. I know two more years seems daunting and insane considering how much your DS enjoys academics. PM me if you ever need support. : )