If Canon makes a lens like that including all features you mentioned , it would not be as cheap as you would like to speand your money on this type of lens.
There is the Nikkor 18-135 , but the Nikkor does not have the VR or VR 2 , I have had one so I know , and it focuses quite slow as compared with Canon USM lenses or Nikkor AF-S (faster kind of it).
The Nikon lens also has alot of CA at 18mm.
Not much better than the Sigma OS lens in terms of IQ and mechanics.
More importantly , the 18mm is not wide enough for an EF-S body like my XTI , it 'd have to be the EF-S17-135 F4 IS USM, if Canon were to replace the EF-S17-85IS, I prefer to have an improved version of the EF-S17-85IS ,though( for a Canon 1.6x crop body, it's important to be 17-xx not 18).
I notice the huge difference between the wide end of my Sigma OS and that of my 17-85IS , plus the 17mm wide end of my 17-85IS is wider than my Sister's 17-55IS and the Sigma's 18mm is not the true 18mm either, it is more like a 19.3 -170mm lens than a 18-200 lens.
It's very important to note the Nikon DX's crop factor is 1.5x, and so the 18mm on any Nikon body would be like 27mm on a FF, but on any 1.6x crop Canon body, the 18mm would be like 29.3mm on a FF body.
I dont think 29mm is wide enough for most of D-SLR shooters as for a walk around zoom, I think this 1mm difference in wide end of zoom is more important than the 50mm longer tele end of the 18-135mm than that of my 17-85IS for most of travel needs.
Actually, while I am traveling many countries , I seldom need any longer than the 85mm end of the lens, but I always want to go much wider than the 17mm end of the lens , so I always compliment this lens with my EF-S10-22.
I thought the OS would be the perfect travel lens for me , but it would not , I simply find the tele end of the lens useless(can not use my 500D close up lens with it) and I dont even use the 100-200 range of it much , when I know I need a tele zoom for a day, I prefer to have my 70-300IS or EF300F4IS wiht me because 200 is not long enough for most of tele photo applications, 300 on a crop body is about 480 on a FF so it is much longer than the 320mm (200x1.6 ) , with 1.4x TC , the 200mm of these Ultra zooms are useless.
And use of the 1.4x TC deteriorate IQ a lot even with these excellent 70-200Ls , so I think the 300 mm end of the 70-300Is is a bit sharper than that of 280 mm end of the 70-200f4 L IS with any 1.4 x TC from any maker.
Also , as you can see from the Size of the OS Sigma and Nikkor VR 18-200, it would be a huge lens if Canon were to make a similar lens with its latest version of IS, and I think its target market would not like the size.
The real reason why Nikon made the AF-S18-135 IF G without the super powerful VR2 probably was to make it reasonably small and cheap, as some people complaining about the size of the AF-S18-200 F3.5-5.6 IF VR2.
And also, Canon is not good at designing this kind of zooms , Nikon, Tamron are definitely better at it since they've been designing and developing this kind of lenses for a long time............
I think next year or end of this year , Tamorn will release VC equipped version of the 18-250 , I would like to replace my Sigma OS with that , I am sure Tamorn won't make it as big as the Sigma OS even with the VC.
Look at their 18-250 , it is even smaller than their 18-200 , and it is much much smaller than the Sigma OS , also, the 200 mm end of Sigma is, as I said many times in many threads ,actually like 170mm , while the Tamorn 200mm end is almost really 200mm...............
I think Canon wants to keep its brand image as professional as it can be, and therefore , the company mostlikely avoid designing this kind of ultra zooms.
Finally, I just bought an Olympus with 18-180 since the new Oly E510IS has in camera IS and it is effective, not like Sony Alpha's useless SSS or Pentax gimmick , and the Oly has the best Dust reduction technology. So although the 18-180 is not wide enough , the E510 and 18-180 combo is the best ultra zoom solution now available ...............
I think if you need an ultra zoom , you should look else where , and keep your Canon for more critical works with more serious lenses.
Try the Oly with the 18-180 ED or Nikon D80 with AF-S18-200VR2 , either of them should be much better than the Sigma OS and XTI or XT combo.