Re: how about a find-library-other-window command?

[Richard Stallman]

    Then after typing `C-x 4 C-c C-f', the prefix `C-x 4' will set some
    special variable, and `show-buffer' called by this command will detect it
    and put `this-command' to the user config alist with a flag to reuse this
    user preference next time this command is called without the prefix `C-x 4'.

That mechanism might work, but that user interface is just no good.
Adding one extra character here is a big change for the worse.

    You have to type `C-x 4 C-x C-f' only once.  After `show-buffer' records the
    fact of calling with the prefix `C-x 4' first time, it will reuse this
    preference on subsequent invocations without the prefix `C-x 4'.

I certainly don't want that.  At least, not as the replacement for the
current C-x 4 prefix.  I don't mind if that behavior is available for
you if you like it, but I won't accept it as the default.