[beating my own drum:]
Indeed, I have a working (rough draft of) realtime collaborative
editing at
https://www.mediawiki.org/wiki/Extension:TogetherJS.
It is quite an interesting UX when you allow realtime "writing at"
each other in this form. Old-timers will remember "ytalk" chats as a
very different sort of discussion, with its own conventions.
At wikimania Erik and I will be presenting two sequential talks (or
maybe one combined talk, TBD) on real-time collaborative mediawiki
editing, and what it would look and feel like and how that would
affect community interactions. (As a brief plug: I would like to make
WP feel more like an active community of *people* and less like a
sterile collection of pages authored by some invisible cabal; from
some previous threads about the "last edit" banner on mobile I'm sure
there are some who prefer the anonymous font of knowledge look. But
ultimately for real-time collaboration to be useful, a prospective
editor needs to find someone to collaborate with...)
Among the interesting issues is how to handle fine-grained attribution
of content/changes in a real-time collaboration. This might also
influence how we feel about fine-grained attribution of comments in a
larger talk page. I look forward to hearing ideas and discussion.
--scott
[weighing in on the nesting/quoting bikeshed: the structured quoting
which Simple Machines Forum (SMF) provides is a nice compromise: it
preserves the exact origin of the quoted material, for easy
backreference, but it also allows flexible editing of the quoted
content and for combining multiple quotations into a single response.]