We've also tried to avoid much acceleration to keep work short and free time long. This has ultimately failed with multiple AP courses in middle school which have lots of busy work that takes time, but early on, school work was truly easy and there was lots of free time to dream and self-teach freely.
I agree that there is no hurry. There may be options for meeting the need without changing the grade level. We've had tutors and independent projects and mentors who were college professors, etc. It's a lot of work, but so far, kids are happy.
I think this is also another path for a child who is not crumbling in school, though as pointed out, it can fall down in middle/high school and takes a lot of work from parents. If the child has an intense outside interest and a happy disposition, it's a good start, IMO. Chess is doing a lot to keep my DS busy/mentally occupied.
