And here I am, just having bought the Tamron 24-70 VC not a year ago...
In all seriousness, if they could make this thing in a not-too-huge package below the $1500 pricepoint, I'd go for it, especially with all the killer lenses sigma's been putting out recently.
I bought one in January and love it. If/when this Sigma comes out and is reviewed I'll strongly consider it. Until then, I am very happy to use the Tamron.
5D Mk III, Elan 7e, Fuji X-E1, some old rangefinders
Tamron 24-70 2.8 VC, Canon 70-200 f/2.8L IS II, 400mm f/2.8L II, 100mm L IS Macro, Sigma 85mm, 50mm, & 35mm f/1.4's, Rokinon 14mm f/2.8, Canon 2x Extender II, Kenko 1.4x, 430 EX II, Elinchroms