I can assure you that we've chosen to pursue higher level learning without changing the actual grade level and have seen no crash and burn or "dysfunctional husk" (like that phrase!).
That's a bit of a red herring, though. I suspect most of us with accelerated kids would not have picked acceleration as the least worst choice if there were meaningful opportunities for higher level learning at school while retaining the same grade designation.
For instance, if we were in a school district to the west of town, rather than to the east of town, my angst would be over whether DD should elect to take Algebra I or pre-Algebra as a sixth grader, neither of which would technically constitute a subject acceleration in that district, not whether she should attempt a subject acceleration in order to be eligible for placement into pre-Algebra, which is only offered as a seventh grade course in our district. If she were in a specific one of the private schools, she'd technically be enrolled as a fifth grader (and would likely have the leeway to be enrolled as a fourth grader, due to summer birthday) while taking the same classes she's in now.
Some kids bloom where they're planted, and will be fine, accelerated or otherwise accommodated or not. Some kids are less tolerant of mismatch. Some kids will crash and burn even in the absence of apparent academic mismatch. My own personal guess, supported only by anecdote, is that temperament is as large a factor as level of giftedness.
