I was baffled by the announcement too... At least tokina listens to their user-base unlike another company "cough, cough" I know...
Possibly because with Tokina, everyone just decides to love on their lenses instead of bickering about everything and having no clue what they like, as is the case with this hypothetical other company. :P
Wow - that surprised me as well. AFS motor, aspherical element, new coating, probably not worth an upgrade but if you don't have a screw drive AF in your body, good update.
I still thing the 12-24 is more versatile - and $500 cheaper.
15mm DOF at 4ft:
f/2.8 = 2'7"
f/4 = 4'2"
I personlly think it's worth upgrading from the 12-24mm f/4 II to the 11-16. AF-S equivalent v. the loud autofocus motor in the 12-24 II is a nice touch, plus for my purposes doing plenty of low light shooting at least the extra stop of aperture is great. Extra 1mm of wide is nice for landscape stuff, this would definitely replace my 12-24 in my travel kit.
Not saying it's necessarily better, since it is a different lens with a different aperture and focal range. Especially now that I have the 24mm f/1.4, I'm not going to miss the 16-24mm range. :)