Default key binding for `mouse-drag-region-rectangle'

[Drew Adams]

This command seems to have been added in Emacs 27
and immediately given the default key binding of
`C-M-down-mouse-1'.

Emacs 27 is still the latest release.  It's likely
that use of this binding isn't yet baked-in for
many users.

I, for one, didn't notice that this had happened
until a few days ago.  I didn't see any discussion
/ proposal about this in emacs-devel.  But I might
have just missed it somehow.  Was this discussed?

IMO, this command should be given a different
default key binding.  (I'm not against giving it
a default binding.)

Can we discuss this?  I suggest giving it the
binding `C-x down-mouse-1' instead.  But mainly
I'd like to see its binding taken off of `C-M-'.

Here are my reasons.

I'd be interested in reasons for binding another
key instead - as well as reasons why someone
thinks this really deserves to be on `C-M-'.

1. There are no other rectangular-region
   commands on `C-M-', and no plans to put any
   others on it.

2. There are sets of related commands that it
   could make sense to put on `C-M-'.  And there
   will be more such, over time.

   `C-M-` is too valuable to waste on a single
   command (i.e., unrelated to others on `C-M-').
   Remaining (unused) `C-M-' bindings should be
   saved for related commands (or at least for
   commands that are repeatable by just holding
   down keyboard keys).

3. `rectangle-mark-mode' is on `C-x SPC'.  This
   is the other rectangle command that involves
   the active region (the only one).

   Its behavior is related to that of the command
   in question (an alternative, in a way).  These
   two commands deserve to be strongly associated
   by their keys.

   The other rectangle commands (which don't
   involve the active region) are also on `C-x'.

   These associations call for the new command to
   be added to the same bunch - same prefix key.
   It makes a good deal of sense to put the new,
   rectangle drag command also on `C-x'.

Could we please consider binding rectangle
definition-by-dragging to `C-x' instead of
`C-M-'?
___

(I filed bug #52130 for this, but that was
immediately closed as "won't fix", with the
reason given as just "Well, I think it makes
sense" - presumably an appeal to authority.)