Well, if nothing else, the rest of your post convinced me that you’re discussing the topic in good faith.
Now, that said, I’ll state outright that I still think you should leave M+ well enough alone. The timer is the core of the mode, and there are plenty of people who like it, and that’s enough reason for it to remain.
If you want something that uses dungeons and scales them, I would encourage you to suggest it as a new dungeon mode entirely separate from M+, as that will completely defuse any possible derailment of the thread. If the idea you pitch has more merit than Mythic+, then that will become clear if/when it is implemented due to the difference in engagement between the two, and that discussion will not be needed at all.
Most of what you have here isn’t very fleshed out, though – for example, I do like that you included puzzles, although I worry that puzzles have little point when the answer can be found via Wowhead or Google – and that’s a problem.
Boss skips are another problematic example. Good idea in theory, but it limits the potential design of the base dungeons. The mode becomes functionally impossible unless every dungeon made to be compatible with the mode includes methods to skip bosses. That creates a design hurdle, which is bad.
I’ve given up on my own attempt because the vast majority of posts (I think it got to 260 or so) were me responding to people, but you’re welcome to use my thread as fodder for ideas.
I tried to do a fair job updating the OP as people contributed, but if you can spare the time, I’d say read the whole thing. It helps provide a picture of the perception problem people have with a timerless mode’s mere discussion, and paints a better picture of where the thinking those who are happy with M+ in its current state is at.
All I would ask is that you don’t actually revive the thread, because in all honesty, I don’t want to maintain it anymore. It was an experiment, and one I consider to have failed. I wanted to see if those who wanted a timerless dungeon mode could support and refine the idea themselves, and I feel it’s been made clear to me that they cannot or will not.
By all means, please change my mind about that if you can. I’d be genuinely pleased. If you decide to tread that path, I’d suggest a new thread, a disclaimer, and a very patient attitude toward the dozens of people who will come into the thread, not read it, and drop one-liners about how you’re bad or M+ is fine despite the fact that you’re not trying to change M+ but rather create an alternative.