To the OP:
In 2010 I thought the 70-300 will get a renewal, since Canon was practically giving it away with bodies, and huge rebates were available even without. Even at that time, the difference between the Nikon and the Canon was apparent. But Canon came out with the L instead, and as Neuro mentioned, it was evident that Canon wanted FF users to go L. 2.5 years, and there's been no new non-L. I don't think it's going to happen.
Just get the Tamron 70-300mm VC USD.
Just make sure you never need to sell it, because selling my Tamron was a real pain!
I am very happy with the 70-300 IS. It can be sharp all the way to 300mm.
You must have an exceptional copy. I found mine not to be so sharp between 250-300.
I think the STM version of the 55-250 may give it run for the money at least for those who do not also have a full frame body.
Agreed. Even the 55-250 non-STM was better than the 70-300 and focused as fast. In fact, as the above post said, the Tamron is a much better lens all around (except for resale value).
Having owned the 70-210mm f/3.5-4.5, 100-300mm f/4.5-5.6 USM and now the 70-300mm f/4-5.6 IS USM I can say that at the long end of each of their ranges the 70-300mm is no better than the other two in IQ. Mid range and at the wide end, I'd give the 70-300mm the advantage (but not by a wide margin). Obviously the 70-300mm has IS which the other two lack, but as far as focusing goes 70-210 and 100-300 are head and shoulders above the 70-300.
Having both the 100-300 and the 70-300, I beg to differ. The 100-300 was fast, but in every other department it sucked. Pretty bad IQ all the way, even if you discount the lack of IS. 70-210, I have no idea about.