It seems you have spent a lot of time to think about Duplicati releases. 
I am at the moment discussing this with Kenneth, too.
Your release cycle seems easy to understand and makes a lot of sense. Actually, we had something versy similar in mind, when we created the different update channels. Nonetheless, the main problem still remains unsolved: Assume you are working on a feature A and a feature B. A is stable after 10 canary releases but B is not. How do you want to release an experimental version then? You cannot remove B from the software. Even if you can, you cannot be sure that this has no bad impact on feature A or anything else.
From my point of view, there is no technical solution to this problem. But you can increase the development and testing speed, so that you get less operlapping work: You work on A and get everything done before B is started. And even if B is started while A is in development, they both should be completed quickly, so that feature C becomes a totally independent, new topic.
I think, if we can use our community power to get the new fixes and features tested quickly, we can also speed up the release cycle and be less cautious with releases than we are today. I hope that we can use the forum and Github to get new releases supported and rolled out much faster than in the past.
As I said, we are still discussing how this could work. Then we come up with a first suggestion. This might not be a final solution but hopefully a step into the right direction. And if we get a bit faster, the second step will make it even better soon