Canon must be well aware by now that they can't just drop a 5D3 with a few tweaks and a bump in ISO. They got raked over the coals by Nikon and their loyal fans with the weak DR in the 5D3.
Only if you define "raked over the coals" as being inundated by customers eager to buy at high prices. The 5D3 outsold everything Nikon had up to the much-newer D750 (which appears to be a pretty good product). Yeah, it's time for a refresh on the 5D3, but Canon seems to have a good handle on matching new bodies to eager markets.