> As a trivial example, everybody is free to put a h1 below a h6. It will "work"… Because there is just no semantic meaning to those names!
Well you took the most obvious counter-example, but there's plenty of semantics in HTML. See for example picture/source element, or audio/video. Both as a user and website operator who deals with people in several languages, i cannot have strong enough words for my appreciation of adding subtitles to a video using just `` without having to modify the media container server-side as previously.
Little features like this may sound insignificant to you if you only use the web for forums and blogposts, but they're in my view a great accessibility/internationalization win. h1-h6, unless used in a serious publication, has indeed no semantic meaning other than "make that one bigger than this one". But for deeper semantics, there's schema.org microdata and indieweb.org microformats, which enable deep interoperability/federation between websites with entirely different tech stacks. I would personally appreciate if either/both were standardized as part of the Web instead of the entire JavaScript craze, but saying the web has no semantics is ignoring decades of innovation in this field with very practical applications and i don't think that's very fair.
> separates again documents and applications(...). Gemini tries to get the document part right I think.
I strongly appreciate this separation, as i'm personally interested in document browsers, not applications platforms (i've already got an OS and desktop environment for that). However, i'm not sure gemini gets it "right" (very subjective). I like that there is a document format focused on plaintext UX, and i very much intend to support it on my websites sooner or later. I'm part of the tildeverse where gemini grew and is nowadays thriving. However, in order to reduce bloat, gemini has pretty much given up on every useful semantic aspect of the web. What's left in gemtext is: one-level lists, three-level headings, and preformatted text (code/quotes).
No more alternative text for linked images (unless you want it displayed for everyone including clients like lagrange which support inline images), no more federated mentions/replies like indieweb.org, no more scraping...
> Only in a model where you don't strive for pixel perfection and customizable behaviors for every piece of rendered content something like semantic meaning of those peaces could arise (...) this model is not the web. Not any more…
I'm not sure that's entirely true. Some part of me agrees with the argument, but on the other hand i don't see a reason why a proper semantic markup couldn't provide a suggested pixel-perfect layout which the browser could freely ignore to make its own. Also, when you disable JavaScript entirely, the web is a very capable semantic document platform.
All in all, i don't have a clear opinion on the topic. But i'm sure it's worth investigating. I'm all ears for resources and projects in such directions (either more semantics in gemini, or less interactive stuff in the web). Thanks for taking the time to come up with a thoughtful answer!