I always watch carefully your videos. You've put so much thought into it, it really shows how you've found the advantages and drawbacks of each solution. I also started experimenting with the first option where you basically need to set up the container, rows and columns first before working on your content. Template-wise, I figured that tracking depth could get complicated quickly, and I abandoned the idea, but it sure looks like the most flexible, less "hacky" way compared the new, third option you're proposing. Sure, it requires thinking about design first before inputting your content, and I'm not sure I would offer that option to most of my clients as it requires some learning and a designer/developer frame of mind ("what's the deal about those rows and container anyway?" is what I'd imagine they'd say), but if I'm the sole editor, I'll love to have that option!
The classic option is of course always a good, although obviously more limited option, that is intuitive and supported out of the box without some clever hack and double modals such as the new, hybrid approach. I can't shake the feeling that the third option is going to be brittle and need an ever-growing set of workarounds for all the use cases out there.
Personally, I've gone a different route. That's probably going to sound half-baked to you, but it might be of interest to some. Instead of trying to cram all the blocks on the same page, I'm using subpages as containers for those blocks. In other words, from the parent page, I loop through all the children to build my page out of this series of containers / sections. So each child page is basically a section of the parent page, where I only need to apply columns, then place my blocks inside. If I need to change the order of those sections, it's just a drag and drop away: I simply move the child page up or down below the parent page.
I've not fully explored the possibility, and I'm still experimenting with this on a couple of sites, but I've found it flexible enough for most of my uses, and easy to code. On each child page, first there's a combo (pro) field that holds the basic design settings for the current section, such as margin, padding, background color, width, etc. Then I set up my columns with a simple text field that holds predefined tags for responsive widths and optionally offsets and additional classes, and inside my blocks. Here's a screenshot (in Spanish, sorry) of something very similar to what you've shown in your video: a text on the left, and image on the right.