That’s technology for you. The 6D Mark II hasn’t even shipped and already Canon Rumors has a note up about a 7D Mark III and 90D expected in the first half of 2018. Here is the link:
It’s listed as [CR2], which means “good information from a known source”. There aren’t a lot of specifics, but it mentions video enhancements and it uses the number “4” and the letter “K” (and not as in “this DSLR is brought to you by...”).
According to Wikipedia, the original 7D was announced in September 2009. The Mk II was announced in September 2014, five years later. If the Mk III is announced in the first half of 2018, that will be only 3-1/2 years since the Mk II.
Similarly, the 70D was announced in July 2013. The 80D was announced in February 2016, just 2-1/2 years later. A 90D announcement in early 2018 would be just over two years since the 80D.
Previously, it seemed that Rebels/xxxD’s were on a 2-year refresh cycle, xxD’s were on a 3-year cycle, and xD’s were on a 4-5 year cycle. It’s well known that the low-end of the DSLR market is being eroded by high quality cell phone cameras. My guess is that Canon is trying to compensate by accelerating their refresh cycles in the enthusiast and pro lines, where buyers would be more inclined to upgrade when something newer and shinier comes along.