We faced a similar issue with DS5. He missed state cutoff, and I opted to enroll him at an Independent School. He was already reading at 2nd grade+ before he started school, and this school allowed subject acceleration, so I thought it was a fine fit.
He was bored at this school even though they are more rigorous than other schools. He was placed at 2nd grade in every subject, while retaining his K "homeroom". But scheduling conflicts etc. resulted in his school proposing he skip to 1st grade. Having skipped grades myself, I didn't want to do it to him. After frantic search on this topic, we decided to go forward with it.
Even though he is smaller than others, he is doing much better now in 1st grade. He is still mostly doing 2nd grade work, but science/social studies are in 1st grade.
As one poster said, you address the current issues and deal with the later ones later. It was worth it for us.
