Pantxo, this really seems to be a good solution, thank you. I have pushed the patch with changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/c6b89c4a9e63

I have changed the status to "Ready for test".

According to his page http://www.danrodney.com/mac/ (see at the bottom), those emacs-like key bindings are enabled in cocoa applications like safari or textedit (the very basic mac text/rtf editor).

About replacements for non-alternate USING_OSX_KEYS :

• META + K (DeleteLineRight): this action is handled by octave so "setKey (0)" is fine as is.
• META (+SHIFT) +E/A => CMD (+SHIFT) +right/left arrow
• META + L (VerticalCentreCaret): I don't know, I'd "setKey (0)".

I don't know what Qt::Key_C | Qt::META is the shortcut of? I'll try to print the "description" attribute when I have access to my mac machine (at work next week).

From what I could see, most (not all) mac specific keys that involve META are "alternateKey", we should thus at least "setAlternateKey (0)" also.

If you think it's worth I can produce a patch that disables all mac specific shortcuts involving META (as in the excerpt from comment #23) or replace META by CTRL.

AFAICS QScintilla has a hard coded value for CMD so I don't think it is possible to instruct it to do the CTRL/META swap.

I think I have found a clue on how to solve the problem. I have made the following change and all offending shortcuts now work:

diff -r a311cf821fb0 libgui/src/m-editor/octave-qscintilla.cc
--- a/libgui/src/m-editor/octave-qscintilla.cc        Thu Jul 17 19:27:42 2014 +0200
+++ b/libgui/src/m-editor/octave-qscintilla.cc        Fri Jul 18 18:01:24 2014 +0200
@@ -65,6 +65,34 @@
   cmd_set->find (QsciCommand::LineDelete)->setKey (0);
   cmd_set->find (QsciCommand::LineCut)->setKey (0);
   cmd_set->find (QsciCommand::LineCopy)->setKey (0);
+  QList< QsciCommand * > cmd_list = cmd_set->commands ();
+  for (int i = 0; i < cmd_list.length (); i++)
+    {
+      int cmd_key = cmd_list.at (i)->key ();
+      switch (cmd_key)
+        {
+          case Qt::Key_C | Qt::META :
+          case Qt::Key_A | Qt::META :
+          case Qt::Key_N | Qt::META :
+          case Qt::Key_P | Qt::META :
+          case Qt::Key_F | Qt::META :
+          case Qt::Key_B | Qt::META :
+          case Qt::Key_V | Qt::META :
+            cmd_list.at (i)->setKey (0);
+        }
+      cmd_key = cmd_list.at (i)->alternateKey ();
+      switch (cmd_key)
+        {
+          case Qt::Key_C | Qt::META :
+          case Qt::Key_A | Qt::META :
+          case Qt::Key_N | Qt::META :
+          case Qt::Key_P | Qt::META :
+          case Qt::Key_F | Qt::META :
+          case Qt::Key_B | Qt::META :
+          case Qt::Key_V | Qt::META :
+            cmd_list.at (i)->setAlternateKey (0);
+        }
+    }
 #else

This is clearly not the right approach. Qscintilla's key/alternateKey should be deleted only when needed, i.e. when octave tries to set a shortcut that is already defined.
Could the shortcut manager check for duplicates not only among octave's but also among qscintilla default keys and alternate keys? 

Sorry for the misinterpretation, the non working shortcuts used to work before my patch. The problem is that preventing Qt to interpret CMD as CTRL I also introduced conflicting shortcuts between Octave an QScintilla standardCommands. If I change "editor paste" to "META(CMD)+ALT+V" it works fine.

QScintilla assumes the CTRL/META swap is on, and defines default shortcuts that involve META key (see qscicommandset.cpp in qscintilla sources). For example META+V triggers "PageDown" which is what I observe when I try to paste.

I guess you mean that triggering the doubly defined actions via shortcuts does not work? Have you chosen same or different shortcuts in main and editor window for these actions?

Pantxo, thanks for the patch. I have pushed it with changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/58f1178f49ef
into the gui-release branch.

Do you have a suggestion concerning the shortcuts for the dock widgets?

Changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/3f6280d0a36b
introduces the possibility to export and import shortcut sets.

First thanks again for this beautiful tool.

For the first default set, if you think the proof of concept from bug #41337 (see comment 17) is acceptable, I can provide a patch for mac. I will have to change many default shortcuts as many of the current ones are already defined as system wide shortcuts on mac (e.g. F9 -> show all applications windows) and thus don't reach octave.

Now about the second set, I am not sure it should be hard coded: it could be read from a shrotcut_settings file. If the shortcut_manager was able to import/export shortcut_settings files (I don't know how hard it is to have such feature), we could have as much base shortcut sets as we want. Those sets (platform specific) could also be produced and shared by octave users.

The user preference for disabling global shortcuts when the terminal has focus (comment #10) was added with changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/f017240310fb

When the editor has focus and is docked, all shortcuts are active.
Disabling the shortcuts when the focus changes to the terminal could become a user preference if desired.

When the terminal gets the focus, almost all shortcuts of the gui are disabled because they could conflict with the freely configurable shortcuts for gnu-readline which is used by the command line interface. Even the default Ctrl+Shift+F does not work when the terminal has focus.

I can confirm this issue with Ctrl+X,Ctrl+F.

If you try, e.g. Ctrl+B,Ctrl+F, everything should work fine. The Ctrl+X is used by "Cut" (you should be able to confirm that when having something selected in the editor). I will extend the check for duplicates to take this case into consideration.

Yes, please post your comments here.

I see platform specific defaults (as they are not covered by the platform specific shortcuts provided by Qt itself) as the next step. The list that is used for storing the shortcuts ans its defaults can easily be initialized depending on the target platform.

At the moment only view menus are already managed by the shortcut-manager. At the moment I am working on the scintilla-internal shortcuts for basic edit functions like duplication of the current etc..

I have pushed changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/086093fbdc1a
which implements a shortcut manager.

The manager includes changing shortcuts via the settings dialog and updating the action's shortcuts. For now, not all actions are using the shortcut manager. If the structure proves to be robust in everyday use I will all the other actions.
This bug report is left open because of those still missing actions.