It seems that everybody has forgotten about how Nikon the route Nikon went with the D3 and D3S.
Both are 12.1 megapixel sensors, but the D3S's sensor was completely new and significantly better. It was the low-light king until the current generation came out. The native ISO range of the D3S was higher than the D3.
If the rumored specs are true, then the native ISO range for the T5i and 70D are much higher than before (100-25,600). Hopefully this means they greatly improved the low light capabilities.
Everybody is blinded by the megapixel war that's been going on. If Canon can do what Nikon did to the D3S, then I welcome these new cameras with open arms. I for one think that 18mp is more than enough.