I'd agree with that I'm very keen to see what the new 7D comes out with purely from an interest in using this lens, that and the extra reach it will give my 300f4L in a relatively light and easy to use long range combo. then my 70-200 would basically live on my 5D2.
I will be getting a 5D3 or 1Dx when they come out, mostly to use with my 70-200 and events and I'm at about 250K shutter actuations on my 1D4. The short end on any crop (70mm=112mm) just feels too cramped.
But.... The MTF charts are strikingly nicer on the 17-55 than on the 24-70, plus you have 4 stops of image stabilization. Also, the 7D will give you greater reach than adding a 1.4 teleconverter to your 300/f4, without the image degradation and the loss of light. Also, the long end of you 70-200 112-320) will be longer than your 300/f4. It's a no-brainer.
It's not either/or... it's BOTH.