A counter-argument to consider: if his executive function is inadequate to the workload in 7th, it's unlikely to be better in 8th. It could be expected to be much worse, because skipping him at this point will likely introduce gaps that require addressing with even more work. This is why grade skips work out so much better in early elementary years - the kids learn almost nothing in those years, so any gaps are few and easily addressed. In hindsight, that 4th-grade skip would have been a lot more convenient.
His desire to skip could be used as a motivating tool, though. "I'm not seeing a kid who can move up a full year right now, and neither is the school. We're seeing a kid who is struggling to keep up in 7th. You want a skip? Prove you can handle it. Do the work. Get those grades up."
His writing weakness could also be more problematic, as the required standards and expected output continue to scale up.
Keep in mind that after a skip, his next school year would then be 9th grade, which is when grades start to really matter. And if he's going for a full IB certificate, there's the issue of the 4000 word extended essay looming ahead.
If this were my child, I think I might elect to use the next year-plus to work on those areas of weakness, in order to put him in position to succeed in high school.
