The infuriating thing about all this is that the FAA do not impose a uniform standard, and there are huge discrepancies in what different airlines will allow on as hand luggage. I used to carry a small tape measure and check the "test bins" or whatever the proper name for them is, into which all hand luggage is supposed to fit. Their were length discrepancies of up to 4" and width discreoancies of 2" between the various ailrlines.
The new templates are supposed to allow an article 5"x15" through, but even there, not all templates are the same. I guess it would be possible to get a Baby Taylor in a soft bag through. Actually, you could put the guitar and the gig bag through separately, and reunite them after they were x-rayed! (As long as that was your only hand luggage).
FWIW I am currently in the process of building my own guitar specifically for travel purposes. It has a detachable neck of my own design, but will look (and hopefully sound!) like an OM when assembled. WHen I travel I will simply crate it and no one would ever know that it was a guitar. If the handlers throw it about, it won't matter.
I would suggest that it is probably not a good idea to put a "FRAGILE" sticker on a guitar case wnen you check it in. The handler is liable to think "Does this guy think I am stupid or something? He thinks I don't know a guitar is fragile ? Well, fuck HIM ! BANG !"