He could skip to 5th... and within a couple/few months, he'll be back in the same pickle.
I do think he'll be in a pickle - but certainly not the SAME pickle...
I say don't worry about if a change is 'enough' but just keep looking at the situation and figuring out what would help him 'learn how to learn' now. It doesn't have to be perfect, just 'good enough.'
Yup on the "good enough." I get lost in over-thinking. I'm not playing chess -- I don't have to try solving everything several moves ahead. (Speaking theoretically, 'cause I can't do it in chess, either.)
I had a nice conversation with a GT-ed specialist working with our school. She's going to explore the grade-skip, because that's what she thinks would be the best "initial" move, and then working with subject acceleration on top of that (keeping on-line math for now). It was a promising conversation...
finally.
This conversation helped considerably.
