I thought about exactly this, and this come up when I was
discussing read-only mode with my friends. Currently it doesn’t
interact well with crdt.el

Currently artist-mode works fine with crdt.el (and it’s fun!), but
if variables like tab-width have different value on different peers
it doesn’t behave well.

That leads me to the idea of synchronizing buffer local variables, and
more generally: (copied from my post on /r/emacs)

<start quote>

My real long-term objective is Emacs as an collaborative operating system — 
with a few annotations, developer should be able to make any Emacs application 
collaboration-powered. This is based on the observation that lots of Emacs application
is centered around the buffer and buffer-local-variables, and I imagine by implementing 
synchronization primitives for all components in a buffer pretty much everything 
can be made collaborative.

See the crdt-org-sync-overlay-mode as a prototypical example. It's powered by the
synchronization of overlays (also based on CRDT). IMO once the synchronization 
of buffer text, text-properties, overlays, markers and buffer-local-variables (with annotation) 
is all implemented, it could be much more powerful than any existing collaborative environment.

<end quote>

I’m not sure about the idea of letting the server “dictate” anything.
Emotionally I don’t like it — I try to avoid power hierarchy. And technically,
I can synchronize Boolean variable also using CRDT.

> On Oct 21, 2020, at 7:54 PM, Jean Louis <bugs@gnu.support> wrote:
> 
> I do not know why, but often when I go do some personal hygiene, my
> mind get new ideas. I am programming in Emacs Lisp, but not internals
> of Emacs, so I cannot know if following is right or wrong.
> 
> I was thinking of various modes, likes ses-mode for spreadsheet or Org
> mode, there is also artist mode and other kind of special modes.
> 
> It would not be good if client can choose the mode and change it, that
> would influence data, it could be disaster.
> 
> So in that sense, the mode of editing should be set and dictated by
> the server.
> 
> Now, what if client does not have some of the modes? This condition
> also has to be handled, maybe there should be option
> 
> crdt-allow-client-with-non-existant-mode or similar
> 
> As maybe some modes are just fine to be edited on server let us say in
> Org mode, and fundamental mode could be used on client's side.
> 
> From Internet searches and report of my friend, I got impression that
> major collaboration is on spreadsheet, that is why there is Ethercalc
> software, it works online. So if it is on spreadsheets, people wish to
> insert their statistics or reports. Spreadsheets are exactly related
> to this proposal.
> 
> ses-mode handles spreadsheets, there may be dismal spreadsheet, and
> there may be table modes in Emacs.
> 
> For example, in Org mode, table handling, if I press TAB, I can all
> the table nicely aligned, if I press TAB in mail-mode I get several
> spaces, it would not be same thing, you will say more about that.