Denon is usually on a two year cadence, not a single. 3 years for flagships, AFAIK.
Furthermore, jdsmoothie, on avsforum who seems to be kind of a Denon information carrier, says the x6700h is now on the same three year flagship cycle too, and won’t be replaced until 2023.
https://www.avsforum.com/threads/official-2020-denon-avr-owners-thread-faq-posts-1-8.3151088/
At some point Denon is going to run out of features that generate incentive to buy a new AVR. I think they are nearly there.
I bought the x6700h because I wanted 13 channels. I cannot imagine personally wanting more than 13 channels in my current home theater, so more channels aren’t a draw. New, one off, audio codecs are mostly a bust. IMAX enhanced, Auro 3D, whatever else just around the bend — they will be confined to “also ran” status behind Dolby Atmos and DTS X. Outdated receiver app features can be circumvented by a $50 streaming stick.
Really the last bastions for upgrade incentive are
Better Quality Sound, Better Quality Auto EQ, More/newer HDMI ports. Denon is updating their receiver lines 480p UI to 1080p in the next generation I saw in a Sound United Video on YouTube. So figure that will be the 2022/2023 lineup, but I’m not sure that will make anyone “update” their AVR. I personally don’t see much call for 8k when our human eyes can’t even resolve 4k at normal seating distance. We are at a clear threshold of diminishing returns and I’m quite pleased with the amount of product and “future proofing” I found available in the x6700h for my personal HT “wants”! I have upgraded my AVR on average every 3 years over the last 20 years. My last AVR I kept 4 years (x7200wa). This AVR I expect will last me until I need more than one HDMI 2.1 port, which may be 5 years +.
Denon must be somewhat concerned about this slowing upgrade cycle in their business. Likewise the x3700h for around $1k is very near end game status for a lot of people with its 7.2.4 support. I wonder how Denon HQ plans to address this in their 5 year and 10 year planning meetings.