Having read the whole thread now: oof. Thank you Ihor for shepherding that and for the performance improvements!
With regard to the key-bindings straw man. I guess I'm a bit of an outsider on this one, because I started writing org documents by just typing them in and only over time learning some of the bindings. Maybe having an org-markup-mode or something like that would be a way to provide a sandbox for the +recalcitrants+ newcomers? It might also be a nice way to a/b test them on whether the Emacs editing commands really are as good as they think they are (said the evil-mode user). With regard to ... everything else. I guess at this point it is unsurprising that (for lack of a better term) the uninitiated in the dark corners of org syntax frequently think that syntactic extensions are advisable, skipping over the consideration of possible. Given the opportunities that seem to be lurking in the thread, it seems like it would be good to have some examples of how the e.g. texinfo semantic markup could (or could not) be implemented using existing org syntax. The suggestion to use custom link types seems very practical. It requires no new syntax, and is basically fully extensible for semantic markup needs. I say this having recently spent time reworking the paragraph grammar and the lexer needed to enable it in laundry for the 3rd (or is it 4th?) time. Say it with me: No new syntactic forms! We have more than enough syntax to enable all the extensibility that pretty much anyone will ever need (we just have to document how to use it). In-document extensibility of link types might be possible if we get my regularized keyword syntax implemented, if that were done then all the configuration could in-principle live in a setup file (I have a response on the syntax thread drafted, will try to get back to it). Nesting markup inside code or verbatim seems more difficult because they are intentionally terminal. I am also unfamiliar with texinfo so will be of no help with the examples, but I do look forward to them. Best! Tom