Here is an idea for you as you go into that meeting-- if they are seeing his weaknesses not as 2e issues at all, but as age-appropriate ones which are (for him) relative weaknesses, then a radical acceleration might seem like a huge jump to them.
Are there any split level classrooms in which your son's placement (sans skip) would place him into the LOWER grade next year?
That is, a 2/3 classroom?
That way, one plan COULD be for him to complete a full school year next year at an appropriate level for him-- and a decision wouldn't have to be made all at once, but the year might serve as a way to acclimate him to the older peer group, acclimate the administration to his readiness, and allow you and everyone else to help him mitigate any stumbling blocks before he gets into 4th grade.
That kind of thoughtful, slow, we-can-turn-back-if-we-see-red-flags, plan might be an easier sell with teachers and administration.
It also lets your DS test-drive an acceleration in a way that doesn't mean an additional placement shift for him if things don't fit perfectly next year. His maturity will still be fine for the cohort in the classroom (since he's in the age range in that class-- just at the lower side) and the academics on the higher side should provide everyone with a clear picture of how capable he is with the increased academic expectations.
