I think it depends on what you mean by "think of him." For your own sake, sure. No problem. One of the nice things about homeschooling is you can think about your child any way that works for you. Total flexibility!
But as for re-entering a traditional school...it gets a lot more tricky. Not because it can't be done--I have friends whose kids float back and forth between HSing, public schools and private schools almost every year!--but because your child is going to learn at his own pace for a year, and if he was ahead before, he's probably going to RACE ahead this year! My son--who never seemed very math-y to me--was mastering high school geometry last year at age 6! I was so amazed!
Which leads me to another issue...getting out of step with the schools in the sense of asynchronous learning. DS7 was mastering geometry, but he hadn't yet memorized his times tables, so while he was way ahead in one sense, we sure weren't following the traditional path to get there.
Obviously you don't have to approach things this way. You can follow a very traditional curriculum path. We started out that way. But the fact is that it's hard to resist the siren call of independent study. It's hard to resist following your child and his interests as he gets excited about learning again. Unless you have a super-dee-duper school situation already in mind for next year, you may find that it's just not completely practical--let alone desirable!--to go back once you've homeschooled.
With that said, I do have plans for DS7 once he gets beyond my ability to teach him. There's a private GT school in our area that I intend to send him to when he's past my usefulness to him. But even there, I worry about the fit.
I guess the big worry I have is if you teach your DS at the 7th/8th grade level and then put him back into the 4th grade. There's going to be fallout, since that would be like holding him back 3-4 grade levels! It doesn't seem very practical...
