Re: Add -other-{window, frame} variants of project-prefix-map commands

[Juri Linkov]

>>> What makes you think Emacs core can't have such a keymap?
>> I assumed it would be too monumental change.
>
> `other-frame-window` makes an effort to preserve the old behavior.
> Inevitably, there are some changes, but I don't think these are drastic
> enough to qualify as "monumental" or to rule out the change.

It seems the biggest challenge that needs to be solved before making
any changes in core Emacs is how to keep backward-compatibility with
keybindings added by users to the existing keymap ctl-x-4-map.
I guess it should be fine to run -other-window commands from these keymaps
because display-buffer-overriding-action will override their default
behavior but will provide the same outcome.  Then maybe a new command bound
to `C-x 4` could just introspect ctl-x-4-map and run its commands as is.