The odd thing is, from what we see in canon of Ron's behavior, I can't say that his abusing Hermione would be all that surprising. :( Still, given those facts, a party or parties wanting to make trouble would have all sorts of opportunity to do so. I wonder if there are any experts who can undo the oblivations that Hermione has been afflicted with? That would go some way toward reducing the universe of suspects. Mind you, this reader would have trouble expecting such violent behavior from Neville, but he'd consider it a low-order probability rather than a complete impossibility.
Author's response
If it makes you feel better I will say that Neville is nothing more or less than he seems in this chapter. Call him quietly capable. A good one to have at your back when all hell breaks loose.
GG