I'll shut up. I have a feeling that my objection is really with the very idea of unreserved keywords and I have a feeling that there will be rather more people shouting me down if I go off on that particular rant; meanwhile it's 20 years since I used yacc in earnest and it's too hazy to be able to argue about what it is or isn't capable of.
When I set out I was really only hoping to express a preference as a user; on balance I would really rather not have DO IGNORE, if it were possible to avoid, because it's really ugly, but DO UPDATE/DO NOTHING I could just about cope with (and means you don't need to add IGNORE as a keyword, win!), although it still mildly pains me that there's an additional unnecessary word.
But I certainly don't object enough to hold up you guys doing the actual work for my benefit (among others, obviously!).